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#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 list
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;
}

実行結果

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