并查集

畅通工程

 HDU - 1232 

#include<iostream>
#include<cstdio>
using namespace std;
int par[1010];
int find(int x)
{
    if(par[x] != x)
    {
        par[x] = find( par[x] );
    }
    return par[x];
}
int unio(int x,int y)
{
    int a_root = find(x);
    int b_root = find(y);
    if(a_root != b_root) par[a_root] = b_root ;
    return 1;
}
int main()
{
    int n,m;
    while(~scanf("%d",&n)&&n)
    {
        scanf("%d",&m);
        for(int i=1;i<=n;++i) par[i]=i;
        int begin,end;
        int cnt = 0;
        for(int i=0;i<m;++i)
        {
            scanf("%d%d",&begin,&end);
            unio(begin,end);
        }
        for(int i=1;i<=n;++i) 
        if(par[i] == i) ++cnt;    
        printf("%d\n",cnt-1);
    }
    return 0;
}