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[1005];int father[1005];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)==1&&n)    {        scanf("%d",&m);        for(i=0;i<m;i++)        scanf("%d%d",&s[i].x,&s[i].y);        for(i=1;i<=n;i++)        father[i]=i;        for(i=0;i<m;i++)        {            Union(s[i].x,s[i].y);        }        k=0;        for(i=1;i<=n;i++)        {            if(i==father[i])            k++;        }        printf("%d\n",k-1);    }    return 0;}

HDU-1232-畅通工程（并查集）