合并那一步写错了，应该是：
```cpp
int un(int a,int b)
{
int aa=find(a);
int bb=find(b);
if(aa!=bb) return fa[aa]=bb;
}
```
by 青丝、暮成雪 @ 2016-10-14 14:44:28
楼上正解
by Ghost_lzy @ 2016-10-14 14:55:01
@ 青丝、暮成雪 谢谢
by 耗子i @ 2016-10-14 18:01:13
对哒
by 脱氧核苷酸 @ 2016-10-14 18:02:59