题目链接
http://acm.hdu.edu.cn/showproblem.php?pid=1232
考察并查集，（最小生成树）题目很简单
用k记录树根的个数，k-1就是还需要建设的路

#include<iostream>

#include<cstdio>
using namespace std;

struct node

{

    int x,y;

}s[];

int father[];

int Find(int x)

{

    if(x==father[x]) return x;

    father[x]=Find(father[x]);

    return father[x];

}

void Union(int x,int y)

{

    x=Find(x);

    y=Find(y);

    if(x!=y)

    {

        father[x]=y;

    }

}

int main(void)

{

    int n,m,i,j,k,l;

    while(scanf("%d",&n)==&&n)

    {

        scanf("%d",&m);

        for(i=;i<m;i++)

        scanf("%d%d",&s[i].x,&s[i].y);

        for(i=;i<=n;i++)

        father[i]=i;

        for(i=;i<m;i++)

        {

            Union(s[i].x,s[i].y);

        }

        k=;

        for(i=;i<=n;i++)

        {

            if(i==father[i])

            k++;

        }

        printf("%d\n",k-);

    }

    return;

}