C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define maxn 20010

int f[20010];
int n, m;

int find(int v){
if(f[v] == v)return v;
int F = find(f[v]);
f[v] = F;
return F;
}

int main()
{
    while(scanf("%d%d",&n,&m) != EOF){
        for(int i = 1;i <= n; i++)f[i] = i;
        for(int i = 0;i < m; i++){
            int a, b;
            scanf("%d%d",&a,&b);
            int fa = find(a);
            int fb = find(b);
            f[fb] = fa;
        }
        int Q;
        scanf("%d",&Q);
        while(Q--){
            int a, b;
            scanf("%d%d",&a,&b);
            int fa = find(a);
            int fb = find(b);
            if(fa==fb){
                printf("Yes\n");
            }
            else{
                printf("No\n");
            }
        }
    }
    return 0;
}

C++ :

#include<iostream>
#include<cstring>
using namespace std;
int father[200010];
int n,m,q;
int getfather(int);
void merge(int,int);
bool judge(int,int);
void work();
int main()
{
	work();
	return 0;
}
void work()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)father[i]=i;
	int x,y;
	for(int i=1;i<=m;i++)
	{
		cin>>x>>y;
		merge(x,y);
	}
	int q;
	cin>>q;
	for(int i=1;i<=q;i++)
	{
		cin>>x>>y;
		if(judge(x,y))cout<<"Yes"<<endl;
		else cout<<"No"<<endl;
	}
}
int getfather(int x)
{
	if(father[x]==x)return x;
	father[x]=getfather(father[x]);
	return father[x];
}
void merge(int x,int y)
{
	x=getfather(x);
	y=getfather(y);
	father[x]=y;
}
bool judge(int x,int y)
{
	x=getfather(x);
	y=getfather(y);
	if(x==y)return 1;
	else return 0;
}

Pascal :

var
  n,m,i,x,y:longint;
  f:array[0..100000] of longint;

function find(x:longint):longint;
  begin
    if f[x]=x then exit(x);
    f[x]:=find(f[x]);
    exit(f[x]);
  end;

procedure combine(x,y:longint);
  var
    xx,yy:longint;
  begin
    xx:=find(x);
    yy:=find(y);
    if xx<>yy then f[xx]:=yy;
  end;

begin
  readln(n,m);
  for i:=1 to n do
    f[i]:=i;
  for i:=1 to m do
    begin
      readln(x,y);
      combine(x,y);
    end;
  readln(m);
  for i:=1 to m do
    begin
      readln(x,y);
      if find(x)=find(y) then writeln('Yes')
        else writeln('No');
    end;

end.

Java :

import java.util.Scanner;

public class Main{
	static int n,m,t;
	static int []pre;
	static void init(int m) {
		pre=new int[m+1];
		for(int i=0;i<=m;i++) {
			pre[i]=i;
		}
	}
	static int find(int x) {
		if(pre[x]==x) return x;
		return pre[x]=find(pre[x]);
	}
	static void merge(int x,int y) {
		int fx=find(x);
		int fy=find(y);
		if(fx==fy) return;
		pre[fx]=fy;
	}
	public static void main(String[]args) {
		Scanner sc=new Scanner(System.in);
		n=sc.nextInt();
		m=sc.nextInt();
		init(n);
		for(int i=0;i<m;i++) {
			int a1=sc.nextInt();
			int a2=sc.nextInt();
			merge(a1, a2);
		}
		t=sc.nextInt();
		for(int i=0;i<t;i++) {
		 int b1=sc.nextInt();
		 int b2=sc.nextInt();
		 if(find(b2)==find(b1))System.out.println("Yes");
		 else System.out.println("No");
		}
	}
}