sdut2139图结构练习——BFS——从起始点到目标点的最短步数

http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2139

BFS 借助队列 将节点的邻接点依次存入队中

#include <stdio.h>
#include <stdlib.h>
#include<string.h>
int k[1001][1001],f[1001],n,m,p = 0,w;
typedef struct node
{
    int num,y;
}st;
st q[1001];
void inque(int x)
{
    p++;
    q[p].y = x;
    f[x] = 1;
}
int main()
{
    int i,j,a,b;
    while(scanf("%d%d", &n, &m)!=EOF)
    {
        memset(k,0,sizeof(k));
        memset(f,0,sizeof(f));
        memset(q,0,sizeof(q));
        p = 0;
        int flag = 0;
        for(i = 1 ; i <= m ; i++)
        {
            scanf("%d%d", &a, &b);
            k[a][b] = 1;
        }
        inque(n);
        q[p].num = 0;
        w = 0;
        do
        {
            w++;
            for(i = 1 ; i <= n ; i++)
            {
                if(k[q[w].y][i] == 1&&f[i] == 0)
                {
                    inque(i);
                    q[p].num = q[w].num+1;
                    if(i == 1)
                    {
                        flag = 1;
                        break;
                    }
                }
            }
            if(flag == 1)
            break;
        }while(p!=w);
        if(flag == 1)
        printf("%d\n",q[p].num);
        else
        printf("NO\n");
    }
    return 0;
}