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

View Code

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include<string.h>
 4 int k[1001][1001],f[1001],n,m,p = 0,w;
 5 typedef struct node
 6 {
 7     int num,y;
 8 }st;
 9 st q[1001];
10 void inque(int x)
11 {
12     p++;
13     q[p].y = x;
14     f[x] = 1;
15 }
16 int main()
17 {
18     int i,j,a,b;
19     while(scanf("%d%d", &n, &m)!=EOF)
20     {
21         memset(k,0,sizeof(k));
22         memset(f,0,sizeof(f));
23         memset(q,0,sizeof(q));
24         p = 0;
25         int flag = 0;
26         for(i = 1 ; i <= m ; i++)
27         {
28             scanf("%d%d", &a, &b);
29             k[a][b] = 1;
30         }
31         inque(n);
32         q[p].num = 0;
33         w = 0;
34         do
35         {
36             w++;
37             for(i = 1 ; i <= n ; i++)
38             {
39                 if(k[q[w].y][i] == 1&&f[i] == 0)
40                 {
41                     inque(i);
42                     q[p].num = q[w].num+1;
43                     if(i == 1)
44                     {
45                         flag = 1;
46                         break;
47                     }
48                 }
49             }
50             if(flag == 1)
51             break;
52         }while(p!=w);
53         if(flag == 1)
54         printf("%d\n",q[p].num);
55         else
56         printf("NO\n");
57     }
58     return 0;
59 }