hdu 2120 Ice_cream's world I

本题链接：http://acm.hdu.edu.cn/showproblem.php?pid=2120

本题用并查集判断环的个数，AC代码：

#include<stdio.h>int per[1100];int flag;void init(){for(int i=0;i<1100;i++)per[i]=i;}int find(int x){int r=x;while(r!=per[r])r=per[r];int j,i=x;while(i!=r){j=per[i];i=j;per[i]=r;}return r;}void join(int a,int b){int fa=find(a);int fb=find(b);if(fa!=fb)per[fa]=fb;else flag++;}int main(){int n,m;int a,b;while(scanf("%d%d",&n,&m)!=EOF){init();flag=0;for(int i=0;i<m;i++){scanf("%d%d",&a,&b);join(a,b);}printf("%d\n",flag);}return 0;}