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<vector>
using namespace std;

bool DFS(const vector<vector<int> >& G,
         vector<bool>& is_visited, int a, int b, int i) {
    is_visited[a] = true;
    if (a == b) return true;
    if (i >= G[a].size()) return false;
    if (!is_visited[G[a][i]] && DFS(G, is_visited, G[a][i], b, 0)) {
        return true;
    }
    return DFS(G, is_visited, a, b, i + 1);
}

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

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

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }
//


    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        vector<bool> is_visited(n, false);
        if (DFS(G, is_visited, a, b, 0)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v){
  const char* dlm = "";
  for(const auto& x:v) os << exchange(dlm, " ") << x;
  return os;
}
struct UnionFind{
  using val_t=size_t;
  vector<val_t> par;
  explicit UnionFind(size_t n): par(n) {
    iota(begin(par),end(par),0);
  }
  void connect(val_t s, val_t t){
    // par[root(s)]=t;
    par[root(s)]=root(t);
  }
  val_t root(val_t s){
    if(par[s]!=s) par[s]=root(par[s]);
    return par[s];
  }
  bool visit(val_t s, val_t t){
    return root(s)==root(t);
  }
};
int32_t main(){
  size_t n,m; cin>>n>>m;
  UnionFind tree(n);
  size_t s,t;
  // cout<<tree.par<<endl;;
  for(size_t i=0; i<m; ++i){
    cin>>s>>t;
    tree.connect(s,t);
  }
  // cout<<tree.par<<endl;
  size_t q; cin>>q;
  for(size_t i=0; i<q; ++i){
    cin>>s>>t;
    cout<<(tree.visit(s,t)?"yes\n":"no\n");
  }
}

C++: #include <iostream>
#include <vector>
#define eol '\n'
using namespace std;

vector<int> visit;

bool bfs(int s, int t, vector< vector<int> > list) {
  if (s == t) {
    return true;
  }
  
  // visit flag
  visit[s] = 1;
  
  for (int i = 0; i < list[s].size(); i++) {
    int next = list[s][i];
    if (visit[next] == 0) {
      if (bfs(next, t, list)) {
        return true;
      }
    }
  }
  return false;
}

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

  int n,m,s,t,q;
  cin >> n >> m;

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

  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> s >> t;
    visit = vector<int>();
    if (bfs(s,t,list)) {
      cout << "yes" << eol;
    } else {
      cout << "no" << eol;
    }
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define r(i,n) for(auto i=0;i<n;i++)
#define s(c) static_cast<int>((c).size())

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

	set<int> A[n+1];
	int v1, v2;
	r(i, m){
		cin >> v1 >> v2;

		A[v1].insert(v2);
		A[v2].insert(v1);
	}

	//初期の未到達状態は0
	//必要に応じて連結成分ごとに1から順に分類
	int group[n]{};
	stack<int> s;

	int q, groupNum = 0, gn1, gn2;
	cin >> q;
	r(i, q){
		cin >> v1 >> v2;

		if(group[v1] == 0 && group[v2] == 0){
			groupNum++;

			s.push(v1);
			group[v1] = groupNum;

			while(!s.empty()){
				int v = s.top();
				int size = s(A[v]);
				for(int tmp : A[v]){
					if(!group[tmp]){
						s.push(tmp);
						group[tmp] = groupNum;
					}else{
						size--;
					}
				}
				if(!size)
					s.pop();
			}
		}

		gn1 = group[v1];
		gn2 = group[v2];
		//printf("group[%d]=%d, group[%d]=%d: ", v1, gn1, v2, gn2);
		printf(gn1 == gn2 ? "yes\n" : "no\n");
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define MAX 100000
int pa[MAX];
int ra[MAX];
void init(){
  for(int i=0;i<MAX;i++){
    pa[i]=i;
    ra[i]=0;
  }
}

int find(int x){
  if(pa[x]==x)return x;
  else return pa[x]=find(pa[x]);
}

void unite(int x,int y){
  x=find(x),y=find(y);
  if(x==y)return;
  if(ra[x]<ra[y])swap(x,y);
  pa[y]=x;
  if(ra[x]==ra[y])ra[x]++;
}

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

int n,m,q,a,b;
int main(){
  init();
  scanf("%d %d",&n,&m);
  for(int i=0;i<m;i++){
    scanf("%d %d",&a,&b);
    unite(a,b);
  }
  scanf("%d",&q);
  for(int i=0;i<q;i++){
    scanf("%d %d",&a,&b);
    cout<<(same(a,b)?"yes":"no")<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int>G[MAX];
int color[MAX];

void dfs(int r, int c) {
	stack<int>S;
	S.push(r);
	color[r] = c;
	while (!S.empty()) {
		int u = S.top(); S.pop();
		for (int i = 0; i < G[u].size(); i++) {
			int v = G[u][i];
			if (color[v] == NIL) {
				color[v] = c;
				S.push(v);
			}
		}
	}
}

void assignColor() {
	int id = 1;
	for (int i = 0; i < n; i++)color[i] = NIL;
	for (int u = 0; u < n; u++) {
		if (color[u] == NIL)dfs(u, id++);
	}
}
int main() {
	int s, t, m, q;
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> s >> t;
		G[s].push_back(t);
		G[t].push_back(s);
	}
	assignColor();
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> s >> t;
		if (color[s] == color[t]) {
			cout << "yes" << "\n";
		}else {
			cout << "no" << "\n";
		}
	}
	return 0;
}