pku 2524 Ubiquitous Religions

http://poj.org/problem?id=2524

题目分类是分治，我不知道怎么用分治。并查集1y.注意这里每个人最多有一个宗教信仰

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#define maxn 50007
using namespace std;
int f[maxn];
int find(int x)
{
    if (x != f[x])
    f[x] = find(f[x]);
    return f[x];
}
void Union(int x,int y)
{
    x = find(x);
    y = find(y);
    if (x != y)
    f[y] = x;
}
int main()
{
    int i,n,m,count;
    int cas = 1;
    int a,b;
    while (scanf("%d%d",&n,&m))
    {
        if (!n && !m) break;
        for (i = 0; i <= n; ++i)
        f[i] = i;
        for (i = 0; i < m; ++i)
        {
            scanf("%d%d",&a,&b);
            Union(a,b);
        }
        //for (i = 1; i <= n; ++i)
        //printf("%d ",find(i));
        //printf("\n");
        count = 0;
        for (i = 1; i <= n; ++i)
        {
            if (i != find(i))
            count++;
        }
        printf("Case %d: %d\n",cas++,n - count);
    }
    return 0;
}