6 8 5 3 5 2 6 4 5 6 0 0 8 1 7 3 6 2 8 9 7 5 7 4 7 8 7 6 0 0 3 8 6 8 6 4 5 3 5 6 5 2 0 0 -1 -1
Yes Yes No
//flag[i]数组标记i是否出现，FLAG标记是否有环，sum记录集合的个数
#include<stdio.h>
const int N = 100005;
int flag[N], father[N];
void Init()
{
for(int i = 0; i <= 100000; i++)
flag[i] = 0, father[i] = i;
}
int Find(int x)
{
if(x != father[x])
father[x] = Find(father[x]);
return father[x];
}
void Merge(int a, int b)
{
int p = Find(a);
int q = Find(b);
if(p > q)
father[p] = q;
else
father[q] = p;
}
int main()
{
int a, b;
while(~scanf("%d%d",&a,&b))
{
if(a == -1 && b == -1)
break;
Init();
int FLAG = 0;
while(1)
{
if(a == 0 && b == 0)
break;
if(Find(a) == Find(b))
FLAG = 1;
Merge(a,b);
flag[a] = 1, flag[b] = 1;
scanf("%d%d",&a,&b);
}
if(FLAG == 1)
printf("No\n");
else
{
int sum = 0;
for(int i = 0; i <= 100000; i++)
if(flag[i] && father[i] == i)
sum++;
if(sum > 1)
printf("No\n");
else
printf("Yes\n");
}
}
return 0;
}原文：http://blog.csdn.net/lyhvoyage/article/details/19925659