Adjacency list

#include <stdio.h>

#include <stdlib.h>

typedef struct Node {

    int vertex;

    struct Node* next;

} Node;

typedef struct Alist {

    Node* head;

} Alist;

typedef struct Graph {

    int V;

    Alist* array;

} Graph;

Node* newnode(int vertex) {

    Node* new_node = (Node*) malloc(sizeof(Node));

    new_node->vertex = vertex;

    new_node->next = NULL;

    return new_node;

}

Graph* createGraph(int V) {

    Graph* graph = (Graph*) malloc(sizeof(Graph));

    graph->V = V;

    graph->array = (Alist*) malloc(V * sizeof(Alist));

    for (int i = 0; i < V; ++i)

        graph->array[i].head = NULL;

    return graph;

}

void addedge(Graph* graph, int src, int vertex) {

    Node* new_node = newnode(vertex);

    new_node->next = graph->array[src].head;

    graph->array[src].head = new_node;

    new_node = newnode(src);

    new_node->next = graph->array[vertex].head;

    graph->array[vertex].head = new_node;

}

void printGraph(Graph* graph) {

    for (int v = 0; v < graph->V; ++v) {

        Node* tmp = graph->array[v].head;

        printf("Adjacency list of vertex %d\n head ", v);

        while (tmp) {

            printf("-> %d", tmp->vertex);

            tmp = tmp->next;

        }

        printf("\n");

    }

}

// main function

int main() {

    int V, E, src, vertex;

    printf("Enter the number of vertices: ");

    scanf("%d", &V);

    Graph* graph = createGraph(V);

    printf("Enter the number of edges: ");

    scanf("%d", &E);

    printf("Enter the edges as space separated pairs of vertices (0-indexed):\n");

    for (int i = 0; i < E; i++) {

        scanf("%d %d", &src, &vertex);

        addedge(graph, src, vertex);

    }

    printGraph(graph);

    return 0;

}