Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N, M := sc.nextInt(), sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < M; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	group := make([]int, N)
	for i := 0; i < N; i++ {
		group[i] = -1
	}
	var dfs func(cur int)
	dfs = func(cur int) {
		for i := 0; i < len(G[cur]); i++ {
			next := G[cur][i]
			if group[next] == -1 {
				group[next] = group[cur]
				dfs(next)
			}
		}
	}
	num := 0
	for i := 0; i < N; i++ {
		if group[i] == -1 {
			group[i] = num
			dfs(i)
			num++
		}
	}

	Q := sc.nextInt()
	for i := 0; i < Q; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		if group[s] == group[t] {
			fmt.Fprintln(wtr, "yes")
		} else {
			fmt.Fprintln(wtr, "no")
		}
	}
	wtr.Flush()
}

C++: #include<bits/stdc++.h>
using namespace std;

bool dfs(int node, int gole, vector<vector<int> >& adjlist, vector<bool>& used){

    if(node == gole) return true;

    for(int i = 0; i < adjlist[node].size(); i++){
        if(used[adjlist[node][i]] == false){
            used[adjlist[node][i]] = true;
            bool flag = dfs(adjlist[node][i], gole, adjlist, used);
            if(flag) return true;
        }
    }

    return false;
}

int main(){

    int n, m; cin >> n >> m;

    vector<vector<int> > adjlist(n);               

    //入力
    for(int i = 0; i < m; i++){
        int a, b; cin >> a >> b;                   // a ←→ b に辺がある
        adjlist[a].push_back(b);
        adjlist[b].push_back(a);
        
    }

    //質問
    int q; cin >> q;
    for(int i = 0; i < q; i++){
        int a, b; cin >> a >> b;
        
        vector<bool> used(n, false);
        used[a] = true;
        if(dfs(a, b, adjlist, used)) cout << "yes" << endl;
        else cout << "no" << endl;
    }

    return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;

int main(){
	int n,m,q,i,j;
	int s,t;
	vector<int> L(100005,-1);
	cin >> n >> m;
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	for (i=0;i<m;i++){
		cin >> s >> t ;
		if (L[s]!=L[t]){
			int a=L[t];
			for (j=0;j<n;j++){
				if (L[j]==a){
					L[j]=L[s];
				}
			}
		}
	}
	
	cin >> q;
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (L[s]==L[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <functional>
#include <sstream>
#include <string>
#include <utility>
#include <map>
#include <memory>
#include <set>
#include <vector>
#include <deque>
#include <list>
#include <stack>
#include <queue>

using namespace std;

class Friend
{
public:
  int solve();
  void setGroup( vector<vector<int>>& adj, vector<int>& group, int u, int grpid );
};

void Friend::setGroup( vector<vector<int>>& adj, vector<int>& group, int u, int grpid )
{
  if ( group[u] ) return;
  
  group[u] = grpid;
  
  int n = adj[u].size();
  
  for ( auto i = 0; i < n; ++i )
    {
      int v = adj[u][i];
      setGroup( adj, group, v, grpid );
    }

  return;
}

int Friend::solve()
{
  int n, m;
  cin >> n >> m;
  
  vector<vector<int>> adj( n );

  for ( auto i = 0; i < m; ++i )
    {
      int u, v;
      cin >> u >> v;
      adj[u].push_back( v );
      adj[v].push_back( u );
    }

  int grpid = 1;

  vector<int> group( n, 0 );

  for ( auto i = 0; i < n; ++i )
    {
      if ( group[i] == 0)
        {
          setGroup( adj, group, i, grpid++ );
        }
      cout << i << ":" << group[i] << endl;
    }
  
  int q;
  cin >> q;

  
  for ( auto i = 0; i < q; ++i )
    {
      int u, v;
      cin >> u >> v;
      
      if ( group[u] == group[v] )
        cout << "yes" << endl;
      else
        cout << "no" << endl;
    }
  
  return 0;
}

int main()
{
  Friend f;

  f.solve();

  return 0;
}

C++: #include <stdio.h>
#include <stack>
using namespace std;
int G[1000][1000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0) return dfs(i,t); 
    } 
    return false;
}

int main()
{
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            G[i][j] = 0; 
        }  
    } 
    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}