加个压缩就行

#include<bits/stdc++.h>
using namespace std;
int fa[1000000];
int sixseven(int x){
	if(x==fa[x]) 
		return x;
	else
	 	return fa[x]=sixseven(fa[x]);//压缩
}
void merge(int x, int y)
{
	fa[sixseven(x)]=sixseven(y);
}
int main()
{
    int n,m,p;cin>>n>>m>>p;
    for(int i = 1;i <= n;i++){
    	fa[i] = i;
	}
    while(m--)
        {
            int mi,mj;cin>>mi>>mj;
            merge(mi,mj);	
        }
    while(p--)
        {
            int pi,pj;cin>>pi>>pj;
            if(sixseven(pi)==sixseven(pj))
            	cout<<"Yes\n";
            else
            	cout<<"No\n";
        }
}

甚至不用改