This is a C Program to implement Adjacency List. An array of linked lists is used. Size of the array is equal to number of vertices. Let the array be array[]. An entry array[i] represents the linked list of vertices adjacent to the ith vertex. This representation can also be used to represent a weighted graph. The weights of edges can be stored in nodes of linked lists. Following is adjacency list representation of the above graph.
Here is source code of the C Program to Implement Adjacency List. The C program is successfully compiled and run on a Linux system. The program output is also shown below.
// A C Program to demonstrate adjacency list representation of graphs
#include <stdio.h>
#include <stdlib.h>
// A structure to represent an adjacency list node
struct AdjListNode {
int dest;
struct AdjListNode* next;
};
// A structure to represent an adjacency liat
struct AdjList {
struct AdjListNode *head; // pointer to head node of list
};
// A structure to represent a graph. A graph is an array of adjacency lists.
// Size of array will be V (number of vertices in graph)
struct Graph {
int V;
struct AdjList* array;
};
// A utility function to create a new adjacency list node
struct AdjListNode* newAdjListNode(int dest) {
struct AdjListNode* newNode = (struct AdjListNode*) malloc(
sizeof(struct AdjListNode));
newNode->dest = dest;
newNode->next = NULL;
return newNode;
}
// A utility function that creates a graph of V vertices
struct Graph* createGraph(int V) {
struct Graph* graph = (struct Graph*) malloc(sizeof(struct Graph));
graph->V = V;
// Create an array of adjacency lists. Size of array will be V
graph->array = (struct AdjList*) malloc(V * sizeof(struct AdjList));
// Initialize each adjacency list as empty by making head as NULL
int i;
for (i = 0; i < V; ++i)
graph->array[i].head = NULL;
return graph;
}
// Adds an edge to an undirected graph
void addEdge(struct Graph* graph, int src, int dest) {
// Add an edge from src to dest. A new node is added to the adjacency
// list of src. The node is added at the begining
struct AdjListNode* newNode = newAdjListNode(dest);
newNode->next = graph->array[src].head;
graph->array[src].head = newNode;
// Since graph is undirected, add an edge from dest to src also
newNode = newAdjListNode(src);
newNode->next = graph->array[dest].head;
graph->array[dest].head = newNode;
}
// A utility function to print the adjacenncy list representation of graph
void printGraph(struct Graph* graph) {
int v;
for (v = 0; v < graph->V; ++v) {
struct AdjListNode* pCrawl = graph->array[v].head;
printf("\n Adjacency list of vertex %d\n head ", v);
while (pCrawl) {
printf("-> %d", pCrawl->dest);
pCrawl = pCrawl->next;
}
printf("\n");
}
}
// Driver program to test above functions
int main() {
// create the graph given in above fugure
int V = 5;
struct Graph* graph = createGraph(V);
addEdge(graph, 0, 1);
addEdge(graph, 0, 4);
addEdge(graph, 1, 2);
addEdge(graph, 1, 3);
addEdge(graph, 1, 4);
addEdge(graph, 2, 3);
addEdge(graph, 3, 4);
// print the adjacency list representation of the above graph
printGraph(graph);
return 0;
}
Output:
$ gcc AdjacencyList.c $ ./a.out Adjacency list of vertex 0 head -> 4-> 1 Adjacency list of vertex 1 head -> 4-> 3-> 2-> 0 Adjacency list of vertex 2 head -> 3-> 1 Adjacency list of vertex 3 head -> 4-> 2-> 1 Adjacency list of vertex 4 head -> 3-> 1-> 0
Sanfoundry Global Education & Learning Series – 1000 C Programs.
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