Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n); i >= 0; i--)
#define REP(i, m, n) for (int i = (int)(m); i <= (int)(n); i++)
#define REPR(i, m, n) for (int i = (int)(m); i >= (int)(n); i--)
#define all(v) v.begin(), v.end()
typedef long long ll;

using Graph = vector<vector<int> >;

vector<int> seen;

void dfs(const Graph &G, int v, int c){
  seen[v] = c;

  for(int nv : G[v]){
    if(seen[nv] != -1) continue;
    dfs(G, nv, c);
  }
}

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

  Graph G(n);
  rep(i, m){
    int a, b; cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
  }

  seen.assign(n, -1);
  int c = 0;
  rep(i, n){
    if(seen[i] == -1){
      dfs(G, i, c);
      c++;
    }
  }

  int q; cin >> q;
  rep(i, q){
    int s, t; cin >> s >> t;
    cout << (seen[s] == seen[t] ? "yes" : "no") << endl;
  }

  return 0;
}

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

int main()
{
	int n, m;
	cin >> n >> m;
	vector<vector<int>> g( n );
	for( int i = 0; i < m; i++ ) {
		int s, t;
		cin >> s >> t;
		g[s].push_back( t );
		g[t].push_back( s );
	}
	vector<int> color( n );
	int col = 0;
	for( int i = 0; i < n; i++ ) {
		if( color[i] > 0 ) continue;
		col++;
		color[i] = col;
		queue<int> que;
		que.push( i );
		while( !que.empty() ) {
			int u = que.front();
			que.pop();
			for( auto v : g[u] ) {
				if( color[v] > 0 ) continue;
				que.push( v );
				color[v] = col;
			}
		}
	}

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

C++: #include<iostream>
#include<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<tuple>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;

typedef pair<int, int> P;

void dfs(int s, int group, int n, vector<vector<int>> v, vector<int> &used) {
	used[s] = group;
	int k = v[s].size();
	REP(l, k) {
		int j = v[s][l];
		if (!used[j]) {
			dfs(j, group, n, v, used);
		}
	}
}

void divide(int n, vector<vector<int>> v, vector<int> &used) {
	int s = 0;
	int group = 1;
	while (s < n) {
		dfs(s, group++, n, v, used);
		while (s < n && used[s]) s++;
	}
}

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

	int n, m;
	cin >> n >> m;
	vector<vector<int>> v(n);
	REP(i, m) {
		int s, t;
		cin >> s >> t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	vector<int> used(n, 0);
	divide(n, v, used);
	int q;
	cin >> q;
	REP(i, q) {
		int s, t;
		cin >> s >> t;
		if (used[s] == used[t]) cout << "yes\n";
		else cout << "no\n";
	}
	

	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" << endl; 
        }else{
            cout << "no" << endl;
        }
    }

    return 0;
}

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

const int MAX = 100000;
vector<int> friends[MAX + 1];
int groups[MAX + 1];

void dfs(int id, int gid) {
  if (groups[id] != -1) return;
  groups[id] = gid;

  int l = friends[id].size();
  for (int i = 0; i < l; i++) {
    dfs(friends[id][i], gid);
  }
}

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

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

  int a, b, q;
  int gid = 0;

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

  for (int i = 0; i < n; i++) groups[i] = -1;

  for (int i = 0; i < n; i++) {
    if (groups[i] == -1) dfs(i, gid++);
  }

  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> a >> b;
    if (groups[a] == groups[b]) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  for (int i = 0; i < n; i++) {
    cout << i << ":" << groups[i] << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<queue>

const static int MAX = 100000;
int color[MAX];
int group_color;
std::vector<int> A[MAX];

int search(int o){
    if(color[o] != 0){
	return 0;
    }
    std::queue<int> qu;
    qu.push(o);
    color[o] = group_color;
    while(!qu.empty()){
	int cur = qu.front();
	qu.pop();
	for(int i = 0; i < A[cur].size(); i++){
	    if(color[A[cur][i]] == 0){
		qu.push(A[cur][i]);
	    	color[A[cur][i]] = group_color;
	    }
	}
    }
    return 0;
}

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

    std::cin >> n >> m;
    for(int i = 0; i < m; i++){
	std::cin >> s >> t;
	A[s].push_back(t);
	A[t].push_back(s);
    }
    for(int i = 0; i < n; i++){
        color[i] = 0;
    }
    group_color = 1;
    for(int i = 0; i < n; i++){
	search(i);
	group_color++;
    }

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

    return 0;
}