HDU1272 迷宫通路数

 1 #include <iostream>
 2 #include<stdio.h>
 3 #include<cstring>
 4 
 5 using namespace std;
 6 #define MAXN 100100
 7 int fa[MAXN];
 8 int sign[MAXN];
 9 int flag;
10 
11 int getHead(int a)
12 {
13     while(a!=fa[a]) a=fa[a];
14     return a;
15 }
16 
17 void uni(int x,int y)
18 {
19     int fa_x=getHead(x);
20     int fa_y=getHead(y);
21     if(fa_x==fa_y) flag=0;
22     else fa[fa_x]=fa_y;
23 }
24 
25 int main()
26 {
27     int A,B;
28     while(1){
29         memset(fa,0,sizeof(fa));
30         memset(sign,0,sizeof(sign));
31         scanf("%d%d",&A,&B);
32         if(A==-1&&B==-1) break;
33         if(A==0&&B==0) {
34             printf("Yes\n\n");
35             continue;
36         }
37 
38         fa[A]=A,fa[B]=A;
39         sign[A]=1,sign[B]=1;
40 
41         flag=1;
42         while(scanf("%d%d",&A,&B)&&A!=0&&B!=0){
43             if(!sign[A]) sign[A]=1,fa[A]=A;
44             if(!sign[B]) sign[B]=1,fa[B]=B;
45             uni(A,B);
46         }
47 
48         int k=0;
49         for(int i=1;i<MAXN;i++)
50             if(sign[i]&&fa[i]==i) k++;
51         if(k>1) flag=0;
52         if(flag==0) printf("No\n\n");
53         else printf("Yes\n\n");
54     }
55 
56 
57     return 0;
58 }