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>
#define ll long long
#define INF 999999999
#define MOD 1000000007

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100000;

int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[i] = 0;
	}
}

int find(int x){		//??¨??????????±???????
	if(par[x] == x){
		return x;
	}else{
		return par[x] = find(par[x]);
	}
}

void unite(int x,int y){
	x = find(x);
	y = find(y);
	if(x == y) return;
	if(rank[x] < rank[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(rank[x] == rank[y])
			rank[x]++;
	}
}

bool same(int x,int y){
	return find(x) == find(y);
}

int main()
{
	int n,m,q;
	int a,b;
	cin >> n;
	cin >> m;
	initial(n);
	for(int i=0;i<m;i++){
		cin >> a;
		cin >> b;
		unite(a,b);
	}
	cin >> q;
	for(int i=0;i<q;i++){
		cin >> a;
		cin >> b;
		if(same(a.b)){
			cout << "yes\n";
		}else{
			cout << "no\n";
		}
	}
}

C++: #include<iostream>
#include<map>
#include<set>

using namespace std;

int main(){
	int n, m, s, t, q, i, j;
	int id, stc = 0;
	bool answer_yes = false;
	map<int, set<int> > Adj;
	map<int, int> Stack;
	set<int> Check;
	set<int>::iterator it;

	cin >> n >> m;
	for (i = 0; i < m; i++) {
		cin >> s >> t;
		Adj[s].insert(t);
		Adj[t].insert(s);
	}

	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> s >> t;
		
		// calculate
		Stack.insert(pair<int, int>(stc, s));
		Check.insert(s);
		while (!Stack.empty()) {
			id = Stack[stc];
			for (it = Adj[id].begin(); it != Adj[id].end(); it++) {
				if (Check.find(*it) == Check.end()) {
					if (*it == t) {
						answer_yes = true;
						Stack.clear();
						Check.clear();
						stc = 0;
						break;
					}
					stc++;
					Stack.insert(pair<int, int>(stc, *it));
					Check.insert(*it);
					break;
				}
			}
			if (it == Adj[id].end()) {
				Stack.erase(stc);
				stc--;
			}
		}
		if (answer_yes) {
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
		}
		answer_yes = false;

	}
	
	return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <map>
#include <sstream>
#include <vector>

using namespace std;

vector<vector<int>> V;
map<int, int> pre;
map<int, int> post;
map<int, int> cc;
int t = 1;
int ccid = 1;

int _DFS(int v, vector<bool> &visited) {
  pre[v] = t;
  cc[v] = ccid;
  ++t;
  for (int out_nbr_id : V[v]) {
    if (!visited[out_nbr_id]) {
      visited[out_nbr_id] = true;
      _DFS(out_nbr_id, visited);
    }
  }
  post[v] = t;
  ++t;
}

int main() {
  int n, m;
  cin >> n >> m;

  V = vector<vector<int>>(n);

  int s, t;
  for (int i = 0; i < m; ++i) {
    cin >> s >> t;
    V[s].push_back(t);
    V[t].push_back(s);
  }

  vector<bool> visited(n, false);

  for (int i = 0; i < n; ++i) {
    if (!visited[i]) {
      ++ccid;
      visited[i] = true;
      _DFS(i, visited);
    }
  }

  cin >> s; // ignore # of queries

  while (cin >> s >> t) {
    if (cc[s] == cc[t]) {
      cout << "yes\n";
    } else {
      cout << "no\n";
    }
  }
}

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

vector<int> list[100000];
int num[100000];
int n,m;

void bfs(int s,int sign){

  queue<int> Q;
  Q.push(s);

  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(num[temp]==-1){ //未訪問なら
        Q.push(temp); num[temp]=sign;
      }
    }
  }
}
int main(){

  cin>>n>>m;

  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  fill(num,num+100000,-1);
  int q; cin>>q;

  int sign=0;
  for(int i=0;i<n;i++){
    if(num[i]==-1){
      bfs(i,sign++);
    }
  }
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(num[s]==num[t] && (num[s]!=-1 || num[t]!=-1)){
      cout<<"yes\n";
    }else{
      cout<<"no\n";
    }
  }

  for(int i=0;i<n;i++){
    cout<<num[i]<<" ";
  }
}

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

bool is_friend(const vector<vector<int> >& u, int s, int t, vector<int>& searched){
    if (s == t) return true;
    for (int i = 0; i < u[s].size(); i++) {
        if (!searched[u[s][i]]) {
            searched[u[s][i]] = 1;
            if (is_friend(u, u[s][i], t, searched)) return true;
        }
    }
    return false;
}
int main(){
    int n, m;
    cin >> n >> m;
    vector<vector<int> > u(n);
    for (int i = 0; i < m; i++) {
        int s, t;
        cin >> s >> t;
        u[s].push_back(t);
        u[t].push_back(s);
    }
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int s, t;
        cin >> s >> t;
        vector<int> searched(n, 0);
        searched[s] = 1;
        if (is_friend(u, s, t, searched)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}