poj2524(并查集基础基础基础题)

#include<iostream>
#include<string>
#include<algorithm>
#define M 50005
using namespace std;

int pre[M];
int find(int x)   //带状态压缩的查找
{
  int y=x,temp;
  while(y!=pre[y]) y=pre[y];
  while(x!=y)
  {
    temp=pre[x];
    pre[x]=y;
    x=temp;
  }
  return y;
}

void uni(int x,int y)
{
  int px,py;
  px=find(x);
  py=find(y);
  if(px==py) return ;
  else pre[py]=px;
}


int main()
{
  int n,m,t=0,i,x,y,ans;
  while(scanf("%d%d",&n,&m),m!=0&&n!=0)
  {
    for(i=1;i<=n;i++) //初始化
      pre[i]=i;

    while(m--)
    {
      scanf("%d%d",&x,&y);
      uni(x,y); //合并
    }

    ans=0;
    for(i=1;i<=n;i++)
      if(find(i)==i)
        ans++;

    printf("Case %d: %d\n",++t,ans);
  }
  return 0;
}