How do I implement a graph data structure in C?

How do I implement a graph data structure in C?

To implement a graph in C, you can use an adjacency list or an adjacency matrix. Which one would you prefer?

I think an adjacency list would be better. Can you show me how?

Sure! Here's a simple implementation using an adjacency list:

#include <stdio.h>
#include <stdlib.h>

struct Node {
    int vertex;
    struct Node* next;
};

struct Graph {
    int numVertices;
    struct Node** adjLists;
};

struct Node* createNode(int v) {
    struct Node* newNode = malloc(sizeof(struct Node));
    newNode->vertex = v;
    newNode->next = NULL;
    return newNode;
}

struct Graph* createGraph(int vertices) {
    struct Graph* graph = malloc(sizeof(struct Graph));
    graph->numVertices = vertices;
    graph->adjLists = malloc(vertices * sizeof(struct Node*));

    for (int i = 0; i < vertices; i++) {
        graph->adjLists[i] = NULL;
    }
    return graph;
}

void addEdge(struct Graph* graph, int src, int dest) {
    struct Node* newNode = createNode(dest);
    newNode->next = graph->adjLists[src];
    graph->adjLists[src] = newNode;
}

Would you like to see how to add edges or traverse the graph?

Yes, please show me how to add edges.

To add edges, you can use the addEdge function I provided. For example:

addEdge(graph, 0, 1); // Adds an edge from vertex 0 to vertex 1
addEdge(graph, 0, 4); // Adds an edge from vertex 0 to vertex 4
addEdge(graph, 1, 2); // Adds an edge from vertex 1 to vertex 2

This will create directed edges in your graph. Do you want to see how to traverse the graph next?