/* breadth-first traversal by using a queue
 * @method: use queue
 * Graph is stored in an adjacency matrix
 */
#include<stdio.h>
#include<stdlib.h>

#define MAX		10

int queue[MAX];
int front=-1; //队头元素前一个位置
int rear=-1; //队尾元素


void enqueue(int k)
{
	if(rear < MAX-1)
	{
		queue[++rear] = k;
	}
	else
	{
		printf("queue overflow\n");
		exit(-1);
	}
}

int dequeue(void)
{
	if(front == rear)
	{
		printf("queue underflow\n");
		exit(0);
	}
	return queue[++front];
}


/* breadth-first-traverse 
 * @method: 先访问与node相邻的所有节点，并一次入对。再取队中元素做相同操作
 */
void bfs(int x, int visited[], int adj[][MAX], int n)
{
	int i, count;
	int node;
	
	node = x;
	visited[node] = 1;
	printf("visit node %d\n", node);
	count = 1;
	while(count < n)
	{
		for(i=0; i<n; i++)
		{
			if(adj[node][i] == 1 && visited[i] == 0)
			{
				visited[i] = 1;
				printf("visit node %d\n", i);
				count++;
				enqueue(i);
			}
		}
		node = dequeue();
	}
}

main(void)
{
	int adj[MAX][MAX] = {{0, 1, 1, 0, 0},
	 					 {1, 0, 0, 1, 0},
	 					 {1, 0, 0, 0, 1},
	 					 {0, 1, 0, 0, 0},
	 					 {0, 0, 1, 0, 0}
						};
	
	int n = 5;
	char start_node;
	int visited[MAX];
	memset(visited, 0, MAX*sizeof(int));
	//printf("Enter number of nodes in graph: " );
	//scanf("%d", &n);
	//buildGraph(adj, n);
	
	printf("breadth-first traverse, enter the starting node: ");
	while((start_node = getchar()) != EOF)
	{
		getchar();
	    memset(visited, 0, MAX*sizeof(int));
	    printf("recursive: \n");
	    front = -1;//remember to reset queue
	    rear = -1;
		bfs((int)atoi(&start_node), visited, adj, n);
	}
}