并查集(union-find set )

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/****************************************************************
 * C++  并查集
 * date: 2023-6-3
 * author: Alex Li
 * version: 1.2
 * ****************************************************************/
#include <iostream>
using namespace std;


int father[200];
int x,y;
//找x的祖先，通过递归，当到达祖先位置时，返回祖先
int find(int x){
    //不断向上查找祖先
    if(father[x]!=x) return find(father[x]);
    //路径压缩，所有结点指向一个祖先
    //if(father[x]!=x) father[x]=find(father[x]);
    return father[x];
}
//合并祖先
void unionn(int r1,int r2){
    father[r2]=r1;
    }

bool judge(int x,int y){
    x=find(x);
    y=find(y);
    if(x==y)return true;
    else return false;
}

int main(){
    int n,m;
    cin>>n>>m;
    //初始化，每个结点的父结点都试成自己
    for (int i = 1; i <= n; i++)father[i]=i;
    
    
    for (int i = 1; i <= m; i++){
        cin>>x>>y;
        int r1=find(x);
        int r2=find(y);
        if(r1!=r2)unionn(r1,r2);
    }
    cin>>x>>y;
     if(judge(x,y))cout<<"YES";
     else cout<<"NO";
}