The post Knapsack Problem Using Dynamic Programming in C: Optimizing appeared first on Broad-Hurst In Mart.
]]>From understanding the fundamental concept to practical implementation, this guide delves into the intricacies of this problem-solving technique.
The knapsack problem is a well-known optimization dilemma where you must select items from a set with given weights and values to maximize the total value while staying within a weight limit.
Dynamic programming offers a robust solution to this problem by breaking it down into smaller subproblems, calculating their optimal values, and gradually building up the final solution. With dynamic programming, we can indeed solve the knapsack problem efficiently.
Imagine you are embarking on a hiking expedition, and you have a limited backpack capacity. Your goal is to select items from a list of hiking gear with varying weights and values, maximizing the value you carry while not exceeding the backpack’s weight limit.
This scenario represents a classic example of the knapsack problem. Dynamic programming helps you make the optimal gear selection, ensuring you get the most out of your hiking experience.
Discover how to streamline text data in Python with this guide Python Chomp: Streamlining Text Data with rstrip()
Implementing the knapsack problem in C using dynamic programming requires breaking down the problem into smaller subproblems and utilizing memoization to store intermediate results. By following these structured steps, you can efficiently find the optimal solution:
Understand the problem’s constraints, including the weight limit and the available items’ weights and values;
Set up a table to store the results of subproblems. The table size is determined by the number of items and the weight capacity of the knapsack;
Initialize the table with base values, typically zeros, as a starting point;
Iterate through the items, calculating and storing the optimal value for each subproblem based on the previous results;
Once all subproblems are solved, the final solution lies in the last cell of the table. It represents the maximum value that can be achieved within the given weight limit.
By adhering to these steps and employing dynamic programming techniques, you can implement the knapsack problem efficiently in C, making informed decisions when resource allocation is crucial.
Now, let’s put our knowledge into action and solve a practical example of the knapsack problem using dynamic programming in C. Consider a scenario where you have a knapsack with a weight limit of 10 units, and you’re presented with a list of items, each with its weight and value.
Your goal is to select the combination of items that maximizes the total value while staying within the weight limit.
Here’s a simplified representation of the items:
Let’s use dynamic programming to find the optimal selection of items.
We have a knapsack with a weight limit of 10 units and four items with their respective weights and values.
Set up a table to store the results of subproblems. In this case, the table dimensions will be based on the number of items (4) and the weight capacity (10 units). We initialize it as follows:
```
0 1 2 3 4 5 6 7 8 9 10
----------------------------------------------
0 | 0 0 0 0 0 0 0 0 0 0 0
1 | 0 0 12 12 12 12 12 12 12 12 12
2 | 0 10 12 22 22 22 22 22 22 22 22
3 | 0 10 12 22 30 32 42 52 52 52 52
4 | 0 10 15 25 30 32 42 52 57 57 67
```
The first row and first column of the table are initialized to zeros as a starting point.
Iterate through the items and calculate the optimal value for each subproblem based on the previous results. The table is updated as follows:
```
0 1 2 3 4 5 6 7 8 9 10
----------------------------------------------
0 | 0 0 0 0 0 0 0 0 0 0 0
1 | 0 0 12 12 12 12 12 12 12 12 12
2 | 0 10 12 22 22 22 22 22 22 22 22
3 | 0 10 12 22 30 32 42 52 52 52 52
4 | 0 10 15 25 30 32 42 52 57 57 67
```
The final solution is found in the last cell of the table, representing the maximum value that can be achieved within the given weight limit. In this example, the optimal selection includes Item 1 and Item 4, with a total value of $27.
By following these steps, you can efficiently apply dynamic programming to solve the knapsack problem in C, making informed decisions when resource allocation is paramount.
The knapsack problem, when solved using dynamic programming in C, showcases the practicality of this approach in resource allocation and decision-making. Whether you’re optimizing your backpack for a hiking adventure or tackling real-world resource allocation challenges, the structured process of dynamic programming empowers you to make informed choices and maximize your outcomes.
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]]>The post Cheapest Link Algorithm Example: Simplifying the TSP appeared first on Broad-Hurst In Mart.
]]>The fundamental goal is to minimize costs while identifying optimal routes, making TSP a critical problem to address.
The Cheapest Link Algorithm provides a straightforward method for tackling the complexities of TSP. It operates in a few simple steps:
Learn the ins and outs of determining element visibility with our Selenium guide
Selenium Check If Element Is Visible: Mastering Web Testing
To grasp the Cheapest Link Algorithm’s application, let’s consider an example involving five cities (A, B, C, D, and E) and their respective distances. Using this algorithm, we can determine the shortest route:
The Cheapest Link Algorithm proceeds as follows:
The tour’s route becomes: A → B → D → E → A, with a total distance of 29 units.
A deeper dive into the solution showcases its effectiveness. Starting from City A, the algorithm consistently selects the closest unvisited city, ensuring an optimal path.
Let’s dissect our example:
The tour’s path is A → B → D → E → A, with a total distance of 29 units. This exemplifies the Cheapest Link Algorithm’s proficiency in identifying the shortest route among multiple cities.
The Cheapest Link Algorithm’s practicality extends far beyond our example. It finds application in real-world scenarios such as optimizing delivery routes, circuit design, and DNA sequencing. Mastering its principles and applications empowers you to navigate complex optimization challenges in various domains.
This comprehensive example unveils the Cheapest Link Algorithm’s potential for simplifying the Traveling Salesman Problem. Whether you’re streamlining delivery routes, crafting efficient circuits, or exploring genetic sequences, the Cheapest Link Algorithm stands as a reliable tool in your arsenal. Its straightforward approach and proven effectiveness make it a go-to solution for solving intricate optimization puzzles.
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]]>The post Selenium Check If Element Is Visible: A Comprehensive Guide appeared first on Broad-Hurst In Mart.
]]>Element visibility holds paramount importance in web automation for several reasons:
Selenium offers various methods to determine element visibility. Here are practical approaches.
The most straightforward way to check element visibility is by employing the `.is_displayed()` method. It returns a Boolean value, `True` if the element is visible, and `False` if it’s not. Here’s a Python example:
```python
element = driver.find_element(By.ID, "elementID")
if element.is_displayed():
print("The element is visible.")
else:
print("The element is not visible.")
```
In some cases, an element might not exist on the page, leading to a `NoSuchElementException`. To prevent this error, you can gracefully handle exceptions with `try` and `except` blocks:
```python
try:
element = driver.find_element(By.ID, "elementID")
if element is not None and element.is_displayed():
print("The element is visible.")
else:
print("The element is not visible.")
except NoSuchElementException:
print("Element not found on the page.")
```
Discover the world of optimization with the Cheapest Link Algorithm in our article Cheapest Link Algorithm Example: A Practical Approach to TSP
Let’s delve into two practical examples illustrating the significance of checking element visibility.
Imagine a scenario where you need to click a “Submit” button on a registration form. Before clicking, it’s crucial to ensure the button is visible and enabled for user interaction.
```python
submit_button = driver.find_element(By.ID, "submitBtn")
if submit_button.is_displayed() and submit_button.is_enabled():
submit_button.click()
else:
print("The 'Submit' button is not visible or not enabled.")
```
On dynamic web pages, elements may become visible following user actions, such as a mouse click. In such cases, verifying element visibility is essential:
```python
show_more_button = driver.find_element(By.ID, "showMoreBtn")
show_more_button.click()
new_element = driver.find_element(By.ID, "dynamicElement")
if new_element.is_displayed():
print("The new element is visible.")
else:
print("The new element is not visible.")
```
Checking element visibility is a fundamental aspect of web testing and automation with Selenium. It ensures a seamless user experience and enables adaptability to dynamic web environments. Mastering the techniques outlined in this guide empowers you to enhance the reliability and effectiveness of your web testing endeavors.
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]]>The post Greedy Algorithm Python: An Approach to Set Cover Problems appeared first on Broad-Hurst In Mart.
]]>The greedy algorithm is a widely used optimization technique that follows a simple principle: it makes the best possible choice at each step of a problem, without reconsidering previous choices. This algorithm is particularly useful in scenarios where you want to minimize the number of choices while ensuring that the selected choices cover a specific set comprehensively.
The greedy algorithm operates by iteratively selecting the most promising option that contributes to the overall solution.
Here’s a simplified representation of how it works:
The greedy algorithm excels in scenarios where the problem has optimal substructure and the greedy choice property. These properties allow the algorithm to make locally optimal choices that, when combined, lead to a globally optimal solution.
Dive into the world of space optimization with this article Bin Packing Algorithm: Optimizing Space Utilization
The Greedy Algorithm finds application in various fields, ranging from computer science and network design to logistics and resource allocation:
In network design, the greedy algorithm helps identify the optimal placement of network components to minimize costs while maximizing efficiency;
The algorithm is instrumental in data compression, where it selects the most efficient encoding methods to reduce the size of files or data streams;
Scheduling and task assignment benefit from the greedy algorithm by optimizing the allocation of resources to minimize time and cost;
Resource allocation in various industries, such as manufacturing, transportation, and finance, leverages the greedy algorithm to distribute resources efficiently.
In the field of network design, one common application of the greedy algorithm is the construction of minimal spanning trees. A minimal spanning tree connects all nodes within a network with the minimum possible total edge weight.
By selecting the edges with the lowest weights at each step, the greedy algorithm efficiently constructs a network structure that minimizes costs and ensures efficient data flow.
Data compression is essential in various applications, from image and video streaming to file storage. The greedy algorithm is used in Huffman coding, an efficient compression technique that assigns variable-length codes to different characters based on their frequencies in a dataset.
By choosing codes that minimize the overall length of the encoded data, the greedy algorithm ensures effective compression and reduced storage or transmission requirements.
Efficient task scheduling is crucial in optimizing workflows, whether it’s managing a factory’s production line or scheduling jobs on a server. The greedy algorithm helps allocate tasks based on their priorities, deadlines, or resource requirements, ensuring that the most crucial tasks are completed first while minimizing delays and resource underutilization.
In the world of finance, investors often face the challenge of optimizing their investment portfolios. The greedy algorithm can be used to select the most promising set of investments from a larger pool, aiming to maximize returns while adhering to risk constraints. By selecting the most promising assets one at a time, the algorithm helps build a diversified and potentially profitable portfolio.
The greedy algorithm in Python is a versatile decision-making tool that can be applied to a wide range of problems across different fields.
Whether it’s designing efficient networks, compressing data, scheduling tasks, or optimizing investment portfolios, this algorithm simplifies complex decision-making processes and offers a valuable approach to problem-solving. Understanding its principles and applications can lead to more efficient and effective solutions in various domains.
The greedy algorithm in Python is a powerful tool for solving set cover problems and making decisions efficiently. It operates on the principle of making the best local choices, resulting in globally optimal solutions.
Whether you are working on network design, data compression, scheduling, or resource allocation, understanding the greedy algorithm’s principles and applications can streamline your decision-making processes and lead to more efficient solutions.
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]]>The post Bin Packing Algorithm: Unleashing Efficiency Across Fields appeared first on Broad-Hurst In Mart.
]]>In this article, we’ll explore the intricacies of Bin Packing algorithms, shedding light on their inner workings, practical uses, and their transformative impact across industries.
At its core, the Bin Packing Algorithm is a classic optimization technique aimed at packing objects of varying sizes into a finite number of containers or “bins” while minimizing any wasted space. This versatile algorithm finds applications in scenarios where space optimization is paramount:
Imagine the importance of packing products into storage spaces efficiently to reduce storage costs. The Bin Packing Algorithm excels at solving this inventory management challenge;
In the realm of computer programming, efficient memory allocation is a game-changer. This algorithm minimizes wasted memory, enhancing software performance;
The allocation of tasks to servers or machines in a resource-efficient manner is a fundamental concern in modern computing. Bin Packing Algorithms streamline this allocation process;
In the world of logistics and transportation, loading goods into trucks or containers can become a complex puzzle. Bin Packing algorithms simplify this puzzle, saving transportation costs.
In numerous real-world scenarios, efficient space utilization is not just a luxury—it’s a necessity. Squandering space translates to higher costs and inefficiencies. The Bin Packing Algorithm answers this call by finding the most effective way to pack objects into containers.
Explore the power of the Greedy Algorithm in Python in this post Greedy Algorithm Python: Solving Set Cover Problems
The Bin Packing Algorithm operates on a simple principle: fill each bin to capacity, minimizing the number of bins needed to store all items. Here’s a simplified breakdown of its operation:
Bin Packing algorithms serve as invaluable tools with applications across diverse industries. From efficient warehousing and streamlined manufacturing to optimized software development and enhanced logistics, these algorithms lead to cost savings, reduced waste, and heightened operational efficiency.
In the sphere of scheduling and time management, the Bin Packing algorithm is a game-changer. It optimizes daily tasks by determining the most efficient way to schedule activities within fixed time slots, maximizing productivity and making the most of available time.
Manufacturing companies grappling with the cutting stock problem turn to Bin Packing algorithms for solutions. These algorithms optimize the cutting of raw materials, reducing waste, and in turn, production costs.
Digital media relies on the seamless organization of images. Bin Packing Algorithms come to the rescue, efficiently packing images onto screens, ensuring that content is aesthetically presented and organized.
Cloud computing providers utilize Bin Packing algorithms to distribute workloads efficiently across server clusters. This approach minimizes resource underutilization and guarantees high performance, resulting in cost-effective and scalable services for their clients.
The applications of Bin Packing algorithms transcend industry boundaries. Whether you’re managing your time, optimizing manufacturing processes, beautifying digital media, or enhancing cloud computing services, understanding the principles and techniques of these algorithms is a valuable asset.
Bin Packing algorithms empower you to optimize space utilization and resource allocation effectively, fostering efficiency and minimizing waste in your field.
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]]>The post Subset-Sum Problem with Backtracking in C appeared first on Broad-Hurst In Mart.
]]>This article presents a solution for the subset-sum problem using backtracking in the C programming language. Specifically, it will find all possible subsets from a set of integers that sum up to the target value.
typedef void(*subset_sumfn)(const unsigned int *, size_t);
static unsigned int promising(int i, size_t len, unsigned int weight, unsigned int total,
unsigned int target, const unsigned int *weights)
{
return (weight + total >= target) && (weight == target || weight + weights[i + 1] <= target);
}
static unsigned int sum(const unsigned int *weights, size_t len)
{
unsigned int total = 0;
unsigned int i;
for (i = 0; i < len; i++) {
total += weights[i];
}
return total;
}
static void subset_sum_recursive(const unsigned int *weights, size_t len, unsigned int target,
int i, unsigned int weight, unsigned int total, unsigned int *include, subset_sumfn fun)
{
if (promising(i, len, weight, total, target, weights)) {
if (weight == target) {
fun(include, i + 1);
}
else if (i < (int)len - 1){
include[i + 1] = 1;
subset_sum_recursive(weights, len, target, i + 1, weight + weights[i + 1],
total - weights[i + 1], include, fun);
include[i + 1] = 0;
subset_sum_recursive(weights, len, target, i + 1, weight,
total - weights[i + 1], include, fun);
}
}
}
void subset_sum(const unsigned int *weights, size_t len, unsigned int target, subset_sumfn fun)
{
const unsigned int total = sum(weights, len);
unsigned int *include = calloc(len, sizeof(unsigned int));
if (include == NULL) {
return;
}
subset_sum_recursive(weights, len, target, -1, 0, total, include, fun);
free(include);
}
int main(void)
{
unsigned int weights[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
const unsigned int len = sizeof(weights) / sizeof(unsigned int);
const unsigned int target = 7;
subset_sum(weights, len, target, print_vector);
return 0;
}
The result is represented as binary strings that indicate which elements from the initial set belong to the subset. For instance, the initial binary string corresponds to 1 + 2 + 4, resulting in a sum of 7.
The example provided in the code yields the following results:
1 1 0 1
1 0 0 0 0 1
0 1 0 0 1
0 0 1 1
0 0 0 0 0 0 1
The subset-sum problem, though computationally complex, can be tackled using algorithms like backtracking. The provided C code offers a comprehensive approach to finding all subsets that meet a given target sum. On a related note, for those interested in web automation, another article dives into how to execute JavaScript in Python using Selenium.
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]]>The post JavaScript in Selenium: Tips, Tricks, and Best Practices appeared first on Broad-Hurst In Mart.
]]>Before delving into the ‘how’, it’s vital to understand the ‘why’. There are several reasons:
Let’s delve into how you can execute JavaScript within Selenium in various languages:
In the Java programming realm, Selenium offers the WebDriver tool, enabling the execution of JavaScript through the`JavaScriptExecutor` interface. By casting your WebDriver instance to a `JavaScriptExecutor`, you can utilize the `executeScript()` method. This method executes the JavaScript you pass to it and returns an `Object`.
Here’s an example of how you can fetch the title of a web page using JS and Selenium in Java:
String title = ((JavascriptExecutor) driver).executeScript("return document.title;").toString();
Python’s Selenium bindings simplify the process even more. The WebDriver in Python already comes with the `execute_script()` method, making it straightforward to run JavaScript commands.
Here’s how you can get the title of a web page using JS and Selenium in Python:
title = driver.execute_script("return document.title;")
For those using C#, the WebDriver can be cast to an `IJavaScriptExecutor`. This interface provides the `ExecuteScript()` method, which, like in Java, allows you to execute JavaScript and returns an `Object`.
Here’s an example in C#:
String title = ((IJavaScriptExecutor) driver).ExecuteScript("return document.title;").ToString();
Executing JavaScript in your Selenium scripts can open a myriad of opportunities, from manipulating web elements to extracting information that might not be readily accessible using regular Selenium methods. Whichever programming language you use, Selenium offers a straightforward method to run your JavaScript seamlessly. For those keen on exploring more in-depth topics in programming, there’s another article discussing the implementation of a Spanning Forest in C.
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]]>The post C Programming Insights and Techniques appeared first on Broad-Hurst In Mart.
]]>A spanning forest is a collection of spanning trees, each pertaining to a connected component within the graph. It is a vital construct, offering unique insights into the structure of non-connected graphs. In this article, we will delve into the notion of spanning forests, their significance, and the algorithmic approach to finding them.
Graphs come in various shapes and sizes, and not all of them are guaranteed to be connected. In cases where a graph isn’t connected, attempting to find a single spanning tree that encompasses all vertices becomes an impossibility. Instead, we turn to the concept of a spanning forest.
A spanning forest is essentially a set of spanning trees, with each tree representing a connected component within the original graph. Unlike traditional spanning trees, which are defined in terms of vertices, spanning forests focus on edges. Any vertices that are entirely isolated in the original graph will not appear in the spanning forest.
In the realm of graph theory, the absence of connectivity in a graph poses a challenge when attempting to find a spanning tree that covers all its vertices. However, a solution exists in the form of a spanning forest, which consists of multiple spanning trees, one for each connected component within the graph. Unlike traditional connected components, spanning forest components are represented by sets of edges, not vertices. Any isolated vertices within the graph remain absent in the resulting spanning forest.
Constructing a spanning forest is accomplished through the systematic use of the depth-first search algorithm. This process entails repeatedly initiating the algorithm from each unvisited vertex. As this traversal continues, the spanning forest gradually takes shape. Once all vertices associated with edges have been visited, the spanning forest stands complete.
For those interested in implementing this concept, below is a concise C-based representation. The `spanning_forest()` function accepts a graph in edge list format, along with the number of edges (`size`) and vertices (`order`). Additionally, it accommodates a callback function that is invoked with each newly discovered spanning tree. The implementation efficiently employs the `spanning_tree_recursive()` function from the spanning tree algorithm to uncover each individual spanning tree.
#include <stdlib.h>
typedef struct {
unsigned int first;
unsigned int second;
} edge;
typedef void (*treefn)(const unsigned int *, size_t, const edge *, size_t);
void spanning_tree_recursive(const edge *edges, unsigned int size,
unsigned int order, unsigned int *visited, unsigned int *tree,
unsigned int vertex, int edge, unsigned int *len)
{
unsigned int e;
visited[vertex] = 1;
if (edge != -1) {
tree[(*len)++] = edge;
}
for (e = 0; e < size; e++) {
if (edges[e].first == vertex || edges[e].second == vertex) {
unsigned int neighbour = edges[e].first == vertex ?
edges[e].second : edges[e].first;
if (!visited[neighbour]) {
spanning_tree_recursive(edges, size, order, visited, tree,
neighbour, e, len);
}
}
}
}
void spanning_forest(const edge *edges, unsigned int size, unsigned int order,
treefn fun)
{
unsigned int *visited = calloc(order, sizeof(unsigned int));
unsigned int *tree = malloc((order - 1) * sizeof(unsigned int));
unsigned int len, v;
if (visited == NULL || tree == NULL) {
free(visited);
free(tree);
return;
}
for (v = 0; v < order; v++) {
if (!visited[v]) {
len = 0;
spanning_tree_recursive(edges, size, order, visited, tree, v, -1, &len);
if (len > 0) {
fun(tree, len, edges, size);
}
}
}
free(visited);
free(tree);
}
Here’s an illustrative program that identifies the spanning forest of the graph depicted above.
#include <stdio.h>
#include <stdlib.h>
/* Connect two edges */
void edge_connect(edge *edges, unsigned int first, unsigned int second,
unsigned int *pos)
{
edges[*pos].first = first;
edges[*pos].second = second;
(*pos)++;
}
void print(const unsigned int *tree, size_t tree_size, const edge *edges, size_t size)
{
unsigned int e;
for (e = 0; e < tree_size; e++) {
printf("(%u, %u) ", edges[tree[e]].first, edges[tree[e]].second);
}
putchar('\n');
}
int main(void)
{
const unsigned int order = 9; /* Vertices */
const unsigned int size = 8; /* Edges */
edge *edges;
edges = malloc(size * sizeof(edge));
if (edges == NULL) {
return 1;
}
/* Square */
edges[0].first = 0;
edges[0].second = 1;
edges[1].first = 1;
edges[1].second = 2;
edges[2].first = 2;
edges[2].second = 3;
edges[3].first = 3;
edges[3].second = 0;
/* Triangle */
edges[4].first = 4;
edges[4].second = 5;
edges[5].first = 5;
edges[5].second = 6;
edges[6].first = 6;
edges[6].second = 4;
/* Line */
edges[7].first = 7;
edges[7].second = 8;
spanning_forest(edges, size, order, print);
free(edges);
return 0;
}
The output:
(0, 1) (1, 2) (2, 3)
(4, 5) (5, 6)
(7, 8)
Spanning forests are crucial for understanding non-connected graph structures, offering insight into each connected component when a single spanning tree is unfeasible due to lack of connectivity. Using the efficient depth-first search algorithm, we construct spanning forests, revealing the core of each component within the original graph. These forests find applications in network analysis, algorithm design, and other domains, providing a versatile tool to navigate the intricate relationships within graphs, making them indispensable for graph theory enthusiasts and problem solvers. For those interested in delving deeper into algorithmic constructs, our article on hashtables in C offers a comprehensive exploration of data structures, complementing the understanding gained from spanning forests and graph theory.
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]]>The post Hash Table in C using Singly-Linked Lists appeared first on Broad-Hurst In Mart.
]]>Here are the core components of our hash table:
The hash function used in this implementation is the sdbm hash function, which is a simple and effective string hashing function. However, the design allows for a custom hash function to be set, catering to different requirements.
Here’s a sample program:
#include <stdio.h>
#include <string.h>
#include <hashtable.h>
int main(void)
{
hashtable * table;
const char * result;
unsigned int e;
char * elements[] = {"A", "B", "C", "D", "E", "F"};
const unsigned int n = sizeof(elements) / sizeof(const char*);
table = hashtable_create(7, (hashtable_cmpfn)strcmp);
for (e = 0; e < n; e++) {
hashtable_add(table, elements[e]);
}
hashtable_for_each(table, (hashtable_forfn)puts);
for (e = 0; e < n; e++) {
result = hashtable_find(table, elements[e]);
if (result) {
printf("Found: %s\n", result);
}
else {
printf("Couldn't find %s\n", elements[e]);
}
}
printf("The load factor is %.2f\n", hashtable_get_load_factor(table));
for (e = 0; e < n; e++) {
result = hashtable_remove(table, elements[e]);
if (result) {
printf("Removed: %s\n", result);
}
else {
printf("Couldn't remove %s\n", elements[e]);
}
}
hashtable_delete(table);
return 0;
}
The header file:
#include <stdlib.h>
#include <hashtable.h>
hashnode * hashnode_create(void * data)
{
hashnode * node = malloc(sizeof(hashnode));
if (node) {
node->data = data;
node->next = NULL;
}
return node;
}
void hashnode_delete(hashnode * node)
{
free(node);
}
static unsigned long sdbm(const char *str)
{
unsigned long hash = 0;
int c;
while ((c = *str++))
hash = c + (hash << 6) + (hash << 16) - hash;
return hash;
}
hashtable * hashtable_create(size_t size, hashtable_cmpfn compare)
{
hashtable * table = malloc(sizeof (hashtable));
if (table) {
table->size = size;
table->hash = (hashtable_hashfn)sdbm;
table->compare = compare;
table->count = 0;
table->buckets = malloc(size * sizeof(hashnode *));
if (table->buckets) {
unsigned int b;
for (b = 0; b < size; b++) {
table->buckets[b] = NULL;
}
}
else {
free(table);
table = NULL;
}
}
return table;
}
void hashtable_empty(hashtable * table)
{
unsigned int i;
hashnode * temp;
for (i = 0; i < table->size; i++) {
hashnode * current = table->buckets[i];
while (current != NULL) {
temp = current->next;
hashnode_delete(current);
current = temp;
}
table->buckets[i] = NULL;
}
table->count = 0;
}
void hashtable_delete(hashtable * table)
{
if (table) {
hashtable_empty(table);
free(table->buckets);
free(table);
}
}
void * hashtable_add(hashtable * table, void * data)
{
const unsigned int bucket = table->hash(data) % table->size;
void * found = NULL;
if (table->buckets[bucket] == NULL) {
/* An empty bucket */
table->buckets[bucket] = hashnode_create(data);
}
else {
unsigned int added = 0;
hashnode * current, * previous = NULL;
for (current = table->buckets[bucket]; current != NULL && !found && !added; current = current->next) {
const int result = table->compare(current->data, data);
if (result == 0) {
/* Changing an existing entry */
found = current->data;
current->data = data;
}
else if (result > 0) {
/* Add before current */
hashnode * node = hashnode_create(data);
node->next = current;
if (previous == NULL) {
/* Adding at the front */
table->buckets[bucket] = node;
}
else {
previous->next = node;
}
added = 1;
}
previous = current;
}
if (!found && !added && current == NULL) {
/* Adding at the end */
previous->next = hashnode_create(data);
}
}
if (found == NULL) {
table->count++;
}
return found;
}
void * hashtable_find(const hashtable * table, const void * data)
{
hashnode * current;
const unsigned int bucket = table->hash(data) % table->size;
void * found = NULL;
unsigned int passed = 0;
for (current = table->buckets[bucket]; current != NULL && !found && !passed; current = current->next) {
const int result = table->compare(current->data, data);
if (result == 0) {
found = current->data;
}
else if (result > 0) {
passed = 1;
}
}
return found;
}
void * hashtable_remove(hashtable * table, const void * data)
{
hashnode * current, * previous = NULL;
const unsigned int bucket = table->hash(data) % table->size;
void * found = NULL;
unsigned int passed = 0;
current = table->buckets[bucket];
while (current != NULL && !found && !passed) {
const int result = table->compare(current->data, data);
if (result == 0) {
found = current->data;
if (previous == NULL) {
/* Removing the first entry */
table->buckets[bucket] = current->next;
}
else {
previous->next = current->next;
}
hashnode_delete(current);
table->count--;
}
else if (result > 0) {
passed = 1;
}
else {
previous = current;
current = current->next;
}
}
return found;
}
float hashtable_get_load_factor(const hashtable * table)
{
unsigned int touched = 0;
float loadfactor;
unsigned int b;
for (b = 0; b < table->size; b++) {
if (table->buckets[b] != NULL) {
touched++;
}
}
loadfactor = (float)touched / (float)table->size;
return loadfactor;
}
unsigned int hashtable_get_count(const hashtable * table)
{
return table->count;
}
unsigned int hashtable_find_count(const hashtable *table)
{
unsigned int b;
const hashnode *node;
unsigned int count = 0;
for (b = 0; b < table->size; b++) {
for (node = table->buckets[b]; node != NULL; node = node->next) {
count++;
}
}
return count;
}
void hashtable_for_each(const hashtable * table, hashtable_forfn fun)
{
unsigned int b;
for (b = 0; b < table->size; b++) {
const hashnode *node;
for (node = table->buckets[b]; node != NULL; node = node->next) {
fun(node->data);
}
}
}
void hashtable_for_each2(const hashtable * table, hashtable_forfn2 fun, void *data)
{
unsigned int b;
for (b = 0; b < table->size; b++) {
const hashnode *node;
for (node = table->buckets[b]; node != NULL; node = node->next) {
fun(node->data, data);
}
}
}
void hashtable_set_hashfn(hashtable * table, hashtable_hashfn hash)
{
table->hash = hash;
}
Hash tables are an indispensable data structure with a wide variety of applications, from database indexing to caching. This implementation, using singly-linked lists for overflow chains, provides an effective method to handle collisions and offers flexibility with custom hash functions. The functions provided cater to most of the essential operations one might need to perform on a hash table. For those who wish to further explore the intricacies of data structures, our article on the graph data structure in C provides an in-depth look into another fundamental area of computational design and its applications.
The post Hash Table in C using Singly-Linked Lists appeared first on Broad-Hurst In Mart.
]]>The post An In-Depth Look at Graphs in C Programming appeared first on Broad-Hurst In Mart.
]]>A graph is fundamentally composed of elements termed nodes, and the links that intertwine them, known as connections.
Graphs can exhibit a specific orientation, known as directionality. If the connections within a graph exhibit a defined path or direction, it is termed a unidirectional graph or digraph, with these connections being designated as unidirectional connections or pathways. In the context of this discussion, our primary focus will be on unidirectional graphs, meaning whenever we discuss a connection, we are referencing a unidirectional connection. However, it’s essential to note that bidirectional graphs can effortlessly be portrayed as unidirectional graphs by establishing connections between intertwined nodes in a reciprocal manner.
It’s worth noting that representations can often be streamlined if tailored exclusively for bidirectional graphs, and we’ll touch upon this perspective intermittently.
When a node serves as the terminal point of a connection, it is labeled as a proximal node to the origin node of that connection. The origin node is then recognized as being in close connectivity or proximity to the terminal node.
Consider the visual representation below, showcasing a graph comprising 5 nodal points interconnected by 7 links. The connections bridging points A to D and points B to C denote reciprocal linkages, depicted in this context with a dual-directional arrow symbol.
Delving into a more structured delineation, a graph can be characterized as an organized duo, G = <V, L>, where ‘V’ epitomizes the ensemble of nodal points, and ‘L’, symbolizing the collection of linkages, is essentially an ensemble of systematically arranged pairs of nodal points.
To elucidate, the subsequent formulations represent the earlier portrayed graph employing set notation:
V = {A, B, C, D, E}
A = {<A, B>, <A, D>, <B, C>, <C, B>, <D, A>, <D, C>, <D, E>}
For a comprehensive implementation of a graph structure, it’s essential to have a foundational suite of operations to construct, alter, and traverse through the graph, listing nodal points, linkages, and adjacent nodes.
Below are the operations offered by each model. Specifically, the details presented pertain to the primary model, termed ‘graphModel1’:
graph1 *graph1_create(void);
Create an empty graph
void graph1_delete(graph1 *graph);
Delete a graph
vertex *graph1_add(graph1 *graph, const char *name, void *data);
Add a vertex to the graph with a name, and optionally some data
vertex *graph1_get_vertex(const graph1 *graph, const char *name);
Retrieve a vertex by name
void *graph1_remove(graph1 *graph, vertex *vertex);
Remove a vertex
void graph1_add_edge(graph1 *graph, vertex *vertex1, vertex *vertex2);
Create a directed edge between vertex1 and vertex2
void graph1_remove_edge(graph1 *graph, vertex *vertex1, vertex *vertex2);
Remove the directed edge from vertex1 to vertex2
unsigned int graph1_get_adjacent(const graph1 *graph, const vertex *vertex1, const vertex *vertex2);
Determine if there is an edge from vertex1 to vertex2
iterator *graph1_get_neighbours(const graph1 *graph, const vertex *vertex);
Get the neighbours of a vertex
iterator *graph1_get_edges(const graph1 *graph);
Get all of the edges in the graph
iterator *graph1_get_vertices(const graph1 *graph);
Get all of the vertices in the graph
unsigned int graph1_get_neighbour_count(const graph1 *graph, const vertex *vertex);
Get the count of neighbours of a vertex
unsigned int graph1_get_edge_count(const graph1 *graph);
Get the count of edges in the graph
unsigned int graph1_get_vertex_count(const graph1 *graph);
Get the count of vertices in the graph
In all graph representations, a vertex is defined as follows:
typedef struct {
char *name;
void *data;
void *body;
deletefn del;
} vertex;
Please observe the “body” field, primarily used by certain representations (like Adjacency List and Incidence List) to incorporate per-vertex structure.
The following functions are available for vertex manipulation:
const char *vertex_get_name(const vertex *v);
Get the vertex’s name
void *vertex_get_data(const vertex *v);
Get the data associated with a vertex
The internal implementation of edges differs across representations. In fact, in three representations—Adjacency List, Adjacency Matrix, and Incidence Matrix—edges do not exist as internal objects at all. Nevertheless, from the client’s perspective, edges, as enumerated by the iterator returned from the function for retrieving edges, appear as this structure:
typedef struct {
vertex *from;
vertex *to;
} edge;
Here are the functions available for handling edges:
const vertex *edge_get_from(const edge *e);
Get the vertex that is the starting-point of an edge
const vertex * edge_get_to(const edge *e);
Get the vertex that is the end-point of an edge
The program below creates the graph introduced earlier using an intuitive representation known as “graph1.” It proceeds to list the vertices, their neighbors, and edges.
Graphs can be represented in various ways, each method offering unique advantages and use cases. Here are five fundamental approaches to graph representation:
Choosing the right graph representation depends on the specific requirements of your application, such as memory constraints, computational efficiency, and the type of graph you are working with. Each of these methods has its own strengths and weaknesses, making them valuable tools in the field of graph theory and data analysis.
The representation I refer to as the “intuitive” or sometimes the “object-oriented” representation involves directly translating the mathematical definition of a graph into a data type:
#include <stdio.h>
#include <graph1.h>
int main(void)
{
graph1 *graph;
vertex *v;
vertex *A, *B, *C, *D, *E;
iterator *vertices, *edges;
edge *e;
/* Create a graph */
graph = graph1_create();
/* Add vertices */
A = graph1_add(graph, "A", NULL);
B = graph1_add(graph, "B", NULL);
C = graph1_add(graph, "C", NULL);
D = graph1_add(graph, "D", NULL);
E = graph1_add(graph, "E", NULL);
/* Add edges */
graph1_add_edge(graph, A, B);
graph1_add_edge(graph, A, D);
graph1_add_edge(graph, B, C);
graph1_add_edge(graph, C, B);
graph1_add_edge(graph, D, A);
graph1_add_edge(graph, D, C);
graph1_add_edge(graph, D, E);
/* Display */
printf("Vertices (%d) and their neighbours:\n\n", graph1_get_vertex_count(graph));
vertices = graph1_get_vertices(graph);
while ((v = iterator_get(vertices))) {
iterator *neighbours;
vertex *neighbour;
unsigned int n = 0;
printf("%s (%d): ", vertex_get_name(v), graph1_get_neighbour_count(graph, v));
neighbours = graph1_get_neighbours(graph, v);
while ((neighbour = iterator_get(neighbours))) {
printf("%s", vertex_get_name(neighbour));
if (n < graph1_get_neighbour_count(graph, vertex) - 1) {
fputs(", ", stdout);
}
n++;
}
putchar('\n');
iterator_delete(neighbours);
}
putchar('\n');
iterator_delete(vertices);
printf("Edges (%d):\n\n", graph1_get_edge_count(graph));
edges = graph1_get_edges(graph);
while ((e = iterator_get(edges))) {
printf("<%s, %s>\n", vertex_get_name(edge_get_from(e)), vertex_get_name(edge_get_to(e)));
}
putchar('\n');
iterator_delete(edges);
/* Delete */
graph1_delete(graph);
return 0;
}
The edge object is described not as “from” and “to” but rather as “first” and “second,” meaning it represents an unordered pair.
For the graph introduced earlier, the neighbor sets would appear as follows:
A: {B, D}
B: {C}
C: {B}
D: {A, C, E}
E: {}
Simply provide an iterator to access them. In this implementation, the graph argument in the function for retrieving neighbors is rendered unnecessary.
You should sequentially iterate through each vertex’s neighbors and build the edge using the vertex and the respective neighbor.
The graph comprises a collection of vertices and a matrix indexed by vertices. This matrix contains a “1” entry when the vertices are connected.
typedef struct {
set *vertices;
matrix *edges;
} graph3;
The adjacency matrix for the graph introduced earlier would appear as follows:
Because the addition and removal of rows and columns are resource-intensive operations, the adjacency matrix is not well-suited for graphs where vertices are frequently added and removed.
This allows for the removal of half of it, resulting in a triangular matrix.
This is most effective for a graph that is nearly complete, meaning it has a high density of edges.
The matrix can be sparse, aligning memory usage more closely with the number of edges.
Sparse matrices simplify the addition and removal of columns (without block shifts), but necessitate renumbering.
Employing booleans or bits within the matrix can optimize memory usage.
The graph is comprised of vertices and a matrix, similar to the concept of an Adjacency Matrix. However, in this representation, the matrix has dimensions of vertices × edges, where each column holds two non-zero entries, designating both the starting and ending vertices of an edge. This approach offers a more compact representation, especially for graphs with a large number of vertices and a substantial number of edges.
typedef struct {
set *vertices;
matrix *edges;
} graph4;
The incidence matrix for the graph introduced earlier appears as follows (where “1” denotes “from” and “2” denotes “to”):
Similar to the concept of an Adjacency List, this representation involves a set of vertices. However, in contrast to the Adjacency List, each vertex stores a list of the edges for which it serves as the starting point, rather than merely listing neighbors. This approach is particularly well-suited for certain applications and facilitates efficient access to information regarding the edges originating from each vertex.
typedef struct {
set * vertices;
} graph5;
typedef struct {
set *edges;
} vertex_body;
For the graph introduced earlier, the sets of edges would be represented as follows:
A: {<A, B>, <A, D>}
B: {<B, C>}
C: {<C, B>}
D: {<D, A>, <D, C>, <D, E>}
E: {}
This comprehensive exploration into graph data structures sheds light on their fundamental elements, orientation, connectivity, and theoretical underpinnings. With a focus on the C programming language, the piece offers a suite of practical operations for creating, altering, and traversing graphs. By elucidating the nuances of nodes, connections, and their interrelationships, readers are equipped with a profound understanding of graph implementation, serving as a pivotal resource for anyone striving to deepen their grasp on data structures.
The post An In-Depth Look at Graphs in C Programming appeared first on Broad-Hurst In Mart.
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