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<iostream>
#include<cstdio>
#include<stack>
#include<cstring>
#include<vector>
#include<queue>
#include<stack>
#define white 0
#define grey 1
#define nil -1
#define maxn 100000
using namespace std;

vector<int> g[maxn+5];
int color[maxn+5];
int n,m;

void dfs(int s,int t)
{
    stack<int>q;
    q.push(s);
    color[s]=t;
    while(!q.empty())
    {
        int v=q.top();
        q.pop();
        for(int j=0;j<g[v].size();j++)
        {
            int u=g[v][j];
            if(color[u]==nil)
            {
                q.push(u);
                color[u]=t;
            }
        }
    }
}

void work()
{
    int id=1;
    for(int i=0;i<n;i++)
        color[i]=nil;
    for(int i=0;i<n;i++)
        if(color[i]==nil)
           dfs(i,id++);
}

int main()
{
    scanf("%d%d",&n,&m);
    for(int i=0;i<m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        g[x].push_back(y);
        g[y].push_back(x);
    }
    work();

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

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <stdio.h>
#include <cmath>
#include <set>
#include <map>
using namespace std;

vector<vector<int> >g;
int n,m,q;

vector<bool>visited;
bool dfs(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    cin>>n>>m;
    g.resize(n);
    
    for(int i=0;i<m;i++){
        int s,t;
        cin>>s>>t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
    cin>>q;
    if(q>5)return 1;
    for(int i=0;i<q;i++){
        visited.resize(n,false);
        int s,t;
        cin>>s>>t;
        string ret =(dfs(s,t)?"yes":"no");
        cout<<ret<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
using namespace std;
const int MAXN = 100100 ;
inline int read()
{
	int f = 1, x = 0; char c = getchar();
	while (c < '0' || c > '9') {if (c == '-') f = -1; c = getchar();}
	while (c >= '0' && c <= '9') {x = (x << 3) + (x << 1) + c - '0'; c = getchar();}
	return f * x;
}
int f[MAXN], n, m, q;
int getfa(int x)
{
	if (f[x] == x) return f[x];
	return f[x] = getfa(f[x]);
}
int main()
{
	n = read(); m = read();
	for (int i = 0; i < n; ++i) f[i] = i;
	for (int i = 1, u, v; i <= m; ++i)
	{
		u = read(); v = read();
		int fa1 = getfa(u);
		int fa2 = getfa(v);
		if (fa1 != fa2)
			f[fa1] = fa2;
	}
	q = read();
	for (int i = 1; i <= q; ++i)
	{
		int u, v;
		u = read(); v = read();
		int fa1 = getfa(u), fa2 = getfa(v);
		if (fa1 == fa2) cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int n, m;
vector< list<int> > v;
vector<bool> used;

int main(void){
  ios::sync_with_stdio(false);
  cin.tie(0);

  cin >> n >> m;
  v = vector< list<int> >(n, list<int>(0));
  used = vector<bool>(n, false);
  for(int i = 0; i < m; i++){
    int a, b; cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }
  int q; cin >> q;
  for(int i = 0; i < q; i++){
    used = vector<bool>(n, false);
    int a, b; cin >> a >> b;
    bool flg = false;
    queue<int> que;
    que.push(a);
    while(!que.empty()){
      int q = que.front(); que.pop();
      for(list<int>::iterator it = v[q].begin(); it != v[q].end(); it++){
        if(*it == b){
          flg = true;
          break;
        }
        if(used[*it]) continue;
        used[*it] = true;
        que.push(*it);
      }
      if(flg) break;
    }
    if(flg) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <map>
#include <queue>
using namespace std;
int main(){
  int n,m,t1,t2,c[100000]={}; map <int,bool> g[100000];
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>t1>>t2;g[t1][t2]=1;g[t2][t1]=1;
  }
  int l;cin>>l;
  for(int i=0;i<l;i++){
    queue <int> q;
    bool f[100000]={},find=false;
    cin>>t1>>t2;
    if(c[t1]){
      if(c[t1]==c[t2]) cout<<"yes"<<endl;
      else cout<<"no"<<endl;
      continue;
    }
    q.push(t1);f[t1]=true;c[t1]=i+1;
    for(;!q.empty();){
      for(int j=0;j<n;j++) if(g[q.front()][j]&&!f[j]){
          if(j==t2) find=true;
          f[j]=true;c[t2]=i+1;
          q.push(j);
	}
      q.pop();
      if(find) break;
    }
    if(find) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }
  return 0;
}