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;


const int MAX_N = 1000000;
int par[MAX_N];

//syokika
void init(int n){
  for(int i = 0; i < n; i++) par[i] = i;
}

//kinonewomotomeru
int root(int x){
  if(par[x] == x){
    return x;
  }else{
    return par[x] = root(par[x]);
  }
}

//hanntei
bool same(int x, int y){
  return root(x) == root(y);
}

void unite(int x, int y){
  x = root(x);
  y = root(y);
  if(x == y) return;

  par[x] = y;
}

int main(void){

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

  vector<int> adj[n];

  //syokika
  init(n);

  //heigou
  for(int i = 0; i < m; i++){
    int s, t; cin >> s >> t;
    unite(s, t);
  }

  int q; cin >> q;

  for(int i = 0; i < q; i++){
    int s, t; cin >> s >> t;
    if(same(s, t)) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  


  return 0;

}

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

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

void dfs(int v, int id)
{
    stack<int> S;
    S.push(v);
    color[v] = id;
    int u;
    while (!S.empty()) {
        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] = id;
                S.push(v);
            }
        }
    }
}

void assign_color()
{
    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(int argc, char const *argv[])
{
    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);
    }

    assign_color();

    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> s >> t;
        if (color[s] == color[t]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
    return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <stack>
#include <vector>

using namespace std;
const int nil = -1;

int total, n, m, q;

vector<int>* vecs;
typedef int Comm;
Comm* comms;

void find_connection(int from){
	stack<int> stk;
	stk.push(from);

	while(stk.size()){
		int top = stk.top();
		comms[top] = from;
		for(int i=0, sz=vecs[top].size(); i<=sz; ++i){
			if(i==sz){
				stk.pop();
				break;
			}
			if(comms[vecs[top][i]] == nil){
				stk.push(vecs[top][i]);
				break;
			}
		}
	}
}

int main()
{
	scanf("%d %d",&n,&m);
	vecs = new vector<int> [n];
	comms = new Comm [n];

	for(int i=0; i<n; ++i){
		comms[i] = nil;
	}

	for(int i=0; i<m; ++i){
		int id, f;
		scanf("%d %d",&id,&f);
		vecs[id].push_back(f);
		vecs[f].push_back(id);
	}

	scanf("%d",&q);
	for(int i=0; i<q;++i){
		int from, to;
		scanf("%d %d",&from,&to);
		if(comms[from]==nil && comms[to]==nil){
			find_connection(from);
			if(comms[from] == comms[to]){
				cout << "yes" << endl;
			}
			else{
				cout << "no" << endl;
			}
		}
		else if(comms[from] == comms[to]){
			cout << "yes" << endl;
		}
		else{
			cout << "no" << endl;
		}
	}

	delete[] comms;
	delete[] vecs;

	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define ll long long
typedef complex<double> P;

int main() {
  int n, m; cin >> n >> m;
  vector<int> adj[n];

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

  int sd[n] = {1};
  queue<int> que;
  que.push(0);
  int c = 1;

  while (!que.empty()) {
    int v = que.front(); que.pop();

    for (int i = 0; i < adj[v].size(); i++) {
      if(!sd[adj[v][i]]) {
        que.push(adj[v][i]);
        sd[adj[v][i]] = c;
      }
    }

    if(que.empty()) {
      for (int i = 0; i < n; i++) {
        if(!sd[n]) {
          c++;
          que.push(i);
          break;
        }
      }
    }

  }

  int q; cin >> q;
  for (int i = 0; i < q; i++) {
    int s, t; cin >> s >> t;
    if(sd[s] == sd[t]) {
      cout << "yes" << endl;
    }
    else {
      cout << "no" << endl;
    }
  }
}

C++: #include <iostream>
#include <stack>
#include <vector>
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);
      }
    }
  }
}

int main(){
  int m,s,t,q;

  cin>>n>>m;
  for(int i=0;i<n;i++){
    color[i]=NIL;
  }

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

  for(int u=0;u<n;u++){
    int id=1;

    if(color[u]==NIL){
      dfs(u,id++);
    }
  }

  cin>>q;

  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(color[s]==color[t]){
      cout<<"yes"<<endl;
    }
    else{
      cout<<"no"<<endl;
    }
  }
  return 0;
}