HDU

d.n个村庄m条路，求最少修多少条路可以连通所有的村庄

s.并查集求出集合个数，减1即为答案

c.

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;

#define MAXN 1024

int fa[MAXN];

int set_find(int d){
    if(fa[d]<0)return d;
    return fa[d]=set_find(fa[d]);
}

void set_join(int x,int y){
    x=set_find(x);
    y=set_find(y);
    if(x!=y)fa[x]=y;
}

int main(){
    int N,M;
    int x,y;
    while(~scanf("%d",&N)){
        if(N==0)break;
        scanf("%d",&M);

        memset(fa,-1,sizeof(fa));
        for(int i=0;i<M;++i){
            scanf("%d%d",&x,&y);
            set_join(x,y);
        }

        int sum=0;
        for(int i=1;i<=N;++i)
            if(fa[i]==-1)
                ++sum;
        printf("%d
",sum-1);
    }
    return 0;
}