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 frag;

vector<vector<int>> makelist(int n, int m) {
	vector<vector<int>> Adjlist(n);
	int a, b;

	for(int i = 0; i < m; i++) {
		cin >> a >> b;
		Adjlist[a].push_back(b);
		Adjlist[b].push_back(a);
	}

	return Adjlist;
}

void dfs_run(int a, int b, vector<vector<int>>& adj, vector<bool>& checker) {
	//cout << a << endl;
	while(!adj[a].empty()) {
		int tmp;
		tmp = adj[a].back();
		adj[a].pop_back();	
		if(checker[tmp] == false) {
			continue;
		}
		checker[tmp] = false;
		if(tmp == b) {
			frag = true;
		}else{
			dfs_run(tmp, b, adj, checker);
		}
	}
}

bool dfs(int n, int a, int b, vector<vector<int>> adj) {
	vector<bool> checker(n, true);
	
	checker[a] = false;
	dfs_run(a, b, adj, checker);
	return frag;
}

int main(void)
{
	int n, m, q;

	cin >> n >> m;
	vector<vector<int>> Adjlist = makelist(n, m);

	cin >> q;
	for(int i = 0; i < q; i++) {
		int a, b;
		cin >> a >> b;

		frag = false;
		if(dfs(n, a, b, Adjlist)) {
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
#include <stack>
#include <map>
#define FOR(i,b,e) for(int i=b;i<e;i++)
#define REP(i,n) FOR(i,0,n)
using namespace std;

const int N = 100000;
int n, m, q;
vector< vector<int> > M;
bool V[N];

int bfs(int u, int v) {
  int s;
  queue<int> q;
  REP(i, n) V[i] = false;

  s = u;
  q.push(s);
  V[s] = true;

  while (!q.empty() && !V[v]) {
    s = q.front(); q.pop();
    REP(i, n) {
      if (M[s][i] == 1 && !V[i]) {
        q.push(i);
        V[i] = true;
      }
    }
  }

  return V[v];
}

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

  cin >> n >> m;
  REP(i, n) {
    vector<int> vc(n);
    M.push_back(vc);
  }
  REP(i, m) {
    int u, v;
    cin >> u >> v;
    M[u][v] = M[v][u] = 1;
  }

  cin >> q;
  REP(i, q) {
    int u, v;
    string answer;
    cin >> u >> v;
    answer = bfs(u, v) ? "yes" : "no";
    cout << answer << endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <stack>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <string>
#include <cstdio>
#include <queue>
#include <list>
using namespace std;

struct UnionFind{
  vector<int> data;
  UnionFind(int size): data(size, -1){}
  bool unioSet(int x, int y){
    x = root(x); y = root(y);
    if(x != y){
      if(data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y){
    return root(x) == root(y);
  }
  int root(int x){
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x){
    return -data[root(x)];
  }
};

int main(){
  int n, m, q;
  int x, y;
  cin >> n >> m;
  UnionFind uf(n);
  for(int i=0;i<m;i++){
    cin >> x >> y;
    uf.unioSet(x, y);
  }
  cin >> q;
  vector<bool> out(q);
  for(int i=0;i<q;i++){
    cin >> x >> y;
    out[i] = (uf.findSet(x, y));
  }
  for(int i=0;i<q;i++){
    cout << (out[i] ? "yes" : "no") << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<unordered_map>
#include<unordered_set>

using namespace std;

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

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

	/*for (auto it1 = Adj.begin(); it1 != Adj.end(); it1++) {
		cout << "\n" << it1->first << " : " << flush;
		for (auto it2 = it1->second.begin(); it2 != it1->second.end(); it2++) {
			cout << *it2 << " " << flush;
		}
	}
	cout << endl;*/

	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];
			//cout << "\nid : " << id << " stc : " << stc << endl;
			itend = Adj[id].end();
			for (it = Adj[id].begin(); it != itend; it++) {
				//cout << *it << " " << flush;
				if (Check.find(*it) == Check.end()) {
					if (*it == t) {
						answer_yes = true;
						Stack.clear();
						break;
					}
					stc++;
					Stack.insert(pair<int, int>(stc, *it));
					Check.insert(*it);
					break;
				}
			}
			if (it == itend) {
				Stack.erase(stc);
				stc--;
			}
		}
		if (answer_yes) {
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
			Stack.clear();
		}
		answer_yes = false;
		Check.clear();
		stc = 0;
	}
	
	return 0;
}

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

int n,m,q;
int s,t;
int ck[100002];
list<int>l[100002];

int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    l[s].push_back(t);
    l[t].push_back(s);
  }
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    int flag=0;
    
    queue<int>que;
    que.push(s);
    
    for(int j=0;j<100002;j++)ck[j]=0;
    while(que.size()!=0 && flag==0){
      int x=que.front();
      que.pop();
      for(int j=0;j<l[x].size();j++){
	int y=l[x].front();
	l[x].pop_front();
	l[x].push_back(y);
	if(ck[y]==0){
	  ck[y]=1;
	  que.push(y);
	}
	if(y==t){
	  flag=1;
	  break;
	}
      }
    }
    
    if(flag==1)cout<<"yes"<<endl;
    else cout<<"no"<<endl;
    
  }
  
}