hdu 2120 Ice_cream's world I

判断环的个数

#include <stdio.h>
#include <string.h>

#define MAXN 1003

int father[MAXN];

int find(int x)
{
    int i,t;
    for(i=x; father[i]>=0; i=father[i]) ;
    while(x!=i)
    {
        t=father[x];
        father[x]=i;
        x=t;
    }
    return i;
}
bool merge(int x,int y)
{
    int fx=find(x),fy=find(y);
    if(fx==fy) return false;
    if(father[fx]>father[fy])
    {
        father[fy]+=father[fx];
        father[fx]=fy;
    }
    else
    {
        father[fx]+=father[fy];
        father[fy]=fx;
    }
    return true;
}
int main()
{
    int N,M,i,j;
    while(scanf("%d %d",&N,&M)!=EOF)
    {
        memset(father,-1,sizeof(*father)*(N+1));
        int cnt=0;
        while(M--)
        {
            scanf("%d %d",&i,&j);
            if(!merge(i,j)) cnt++;
        }
        printf("%d\n",cnt);
    }
    return 0;
}