sdut2138图结构练习——BFSDFS——判断可达性

刚开始把路径标记给取消了就一直TLE 

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 1 #include <stdio.h>

 2 #include <stdlib.h>

 3 #include<string.h>

 4 int k[1001][1001],f[1001],n,m,a,b,flag,x;

 5 void dfs(int x)

 6 {

 7     int j;

 8     f[x] = 1;

 9     if(flag == 1)

10     return ;

11     for(j = n ;j>=1 ; j-- )

12         if(k[x][j] == 1&&f[j] == 0)

13         {

14             if(j == 1)

15             {

16                 flag = 1;

17                 return;

18             }

19             dfs(j);

20         }

21 }

22 int main()

23 {

24     int i, j;

25     while(scanf("%d%d", &n, &m)!=EOF)

26     {

27         memset(k, 0, sizeof(k));

28         memset(f, 0, sizeof(f));

29         flag = 0;

30         for(i = 1 ; i <= m ; i++)

31         {

32             scanf("%d%d", &a, &b);

33             k[a][b] = 1;

34         }

35         dfs(n);

36         if(flag)

37         printf("YES\n");

38         else

39         printf("NO\n");

40     }

41     return 0;

42 }