http://acm.hdu.edu.cn/showproblem.php?pid=1232
#include<iostream>
#include<set>
using namespace std;
struct Node
{
    int parent;
    int hight;
};
Node village[1001];

int find(int x) //寻找父亲
{
    while(x != village[x].parent)
        x = village[x].parent;
    return x;
}

void merge(int a,int b)
{
    if(village[a].hight == village[b].hight)//树高一样
    {
            village[b].parent = a;
            village[a].hight += 1;
    }
    else if(village[a].hight > village[b].hight) //矮树并入高树
    {
        village[b].parent = a;//并入a
    }
    else
    {
        village[a].parent = b;//并入b
    }
}
int main()
{
    int n;
    while(scanf("%d",&n) && n)
    {
        int m,i,j,a,b,sum = 0;
        
        for(i=1;i<=n;i++)
        {
            village[i].parent = i;
            village[i].hight = 1;
        }
        scanf("%d",&m);
        while(m--)
        {
            scanf("%d%d",&a,&b);
            a = find(a); //寻找a的根节点
            b = find(b); //寻找b的根节点
            if(a!=b) //根节点不一样才合并
                merge(a,b);
        }
        set<int>S; 
        for(i=1;i<=n;i++) //查找有多少个集合
            S.insert(find(i));
        cout<<S.size()-1<<endl;
    }
    return 0;
}