HDU 1272 小希的迷宫

 1 #include<stdio.h>
 2 #include<string.h>
 3 #define maxn 100000
 4 
 5 int pre[maxn], vis[maxn];
 6 int _max, _min;
 7 
 8 int _find(int x)
 9 {
10     if (x == pre[x])
11         return pre[x];
12     else
13         return _find(pre[x]);
14 }
15 
16 int main()
17 {
18     int a, b, i, sign;
19     while(scanf("%d%d",&a,&b),a!=-1||b!=-1){
20         if(a==0 && b==0){
21                printf("Yes\n");
22                continue;
23         }
24         memset(vis,0,sizeof(vis));
25         if(a>b){
26             _min=b; _max=a;
27         }
28         else{
29             _min=a; _max=b;
30         }
31         vis[a] = vis[b] = 1;
32         for(i = 1; i<=maxn; i++)
33             pre[i] = i;
34 
35         sign=0;
36         pre[_find(a)] = _find(b);
37         while(scanf("%d%d", &a, &b), a || b){
38             vis[a] = vis[b] = 1;
39             if(a > _max) _max=a;
40             else if(a < _min) _min=a;
41             if(b > _max) _max=b;
42             else if(b < _min) _min=b;
43 
44             if(_find(a) == _find(b))
45                 sign = 1;
46             else
47                 pre[_find(a)] = _find(b);
48         }
49         if(sign){
50             printf("No\n");
51             continue;
52         }
53         for(i = _min; i <= _max; i++){
54             if(vis[i] && pre[i]==i)
55                 sign++;
56         }
57         if(sign)//如果有多个根节点的话，不连通，也不行
58             printf("Yes\n");
59         else
60             printf("No\n");
61     }
62     return 0;
63 }