Go: package main

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

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	g := make([][]int, n)
	for i := 0; i < n; i++ {
		g[i] = []int{}
		group[i] = -1
	}
	
	fmt.Scan(&m)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < m; 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)
	}
	for i := 0; i < n; i++ {
		if group[i] != -1 {
			continue
		}
		q := []int{i}
		for len(q) > 0 {
			pop := q[0]
			if len(q) > 1 {
				q = q[1:]
			} else {
				q = []int{}
			}
			if group[pop] == -1 {
				q = append(q, g[pop]...)
				group[pop] = i
			}
		}
	}
	sc.Scan()
	q, _ := strconv.Atoi(sc.Text())
	for i := 0; i < q; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if group[s] == group[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func root(i int, group *[]int) int {
	if i == (*group)[i] {
		return i
	}
	(*group)[i] = root((*group)[i], group)
	return (*group)[i]
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<cstdio>
#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(void) {
	int s, t, m, q;

	scanf("%d%d", &n, &m);

	for (int i = 0; i < m; i++) {
		scanf("%d%d", &s, &t);
		G[s].push_back(t);
		G[t].push_back(s);
	}

	assignColor();

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		scanf("%d%d", &s, &t);
		if (color[s] == color[t]) {
			printf("yes\n");
		}
		else {
			printf("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<stdio.h>
#include<queue>
#include<algorithm>

#define MAX 100000

int G[MAX+1][MAX+1];
int n, m;
std::queue<int> Q;


bool bfs(int src, int dest) {
    bool C[MAX];
    for (int i = 0; i < n; ++i) C[i] = false;

    Q.push(src);
    while(!Q.empty()) {
        int cur = Q.front();Q.pop();
        for (int i = 0; i < n; ++i) {
            if (G[cur][i] == 0) continue;
            if (C[i]) continue;
            if (i == dest) return true;
            Q.push(i);
            C[i] = true;
        }
    }

    return false;
}

int main() {
    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            G[i][j] = 0;
        }
    }
    for (int i = 0; i < m; ++i) {
        int u,k;
        scanf("%d %d", &u, &k);
        G[u][k] = 1;
        G[k][u] = 1;
    }

    int q;
    scanf("%d", &q);
    for (int i = 1; i <= q; ++i) {
        int s,d;
        scanf("%d %d", &s, &d);
        bfs(s, d) ? printf("yes\n") : printf("no\n");
    }

}

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

int main()
{
 int i;
}

C++: #include<iostream>
#include<vector>
#include<stack>
#include<queue>
#include<algorithm>
#include<ctime>

void dfs(std::vector<std::vector<int> > &n) {
	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		std::stack<int> s;
		std::vector<int> went(n.size(), 0);

		s.push(from);
		bool flag = false;
		while (s.size() != 0 && flag == false){
			int num = s.top(); s.pop();
			for (size_t j = 0; j < n[num].size(); j++) {
				if (n[num][j] == to) {
					flag = true;
					break;
				}
				if (went[n[num][j]] == 0) {
					s.push(n[num][j]);
					went[n[num][j]] = 1;
				}
			}
		}
		if (flag) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}
}

int main() {
	int people, relation;

	std::cin >> people >> relation;

	std::vector<std::vector<int> > n(people);

	for (int i = 0; i < relation; i++) {
		int from, to;
		std::cin >> from >> to;
		n[from].push_back(to);
		n[to].push_back(from);
	}

	dfs(n);

	return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
#define MAX 50000

struct Node{
	int group;
	queue<int> fr;
};

int N, M, Q, group_num = 0;
Node person[MAX];

void isFriend(int a, int b){
	if(person[a].group < 0 && person[b].group < 0){
		int p = a, next, m;
		queue<int> move;
		group_num++;
		person[p].group = group_num;
		//cout << a << " is group " << person[a].group << endl;
		move.push(p);

		while(!move.empty()){
			p = move.front();
			if(person[p].fr.empty()){
				move.pop();
			} else {
				m = person[p].fr.size();
				while(m--){
					next = person[p].fr.front();
					person[p].fr.pop();
					if(person[next].group < 0){
						person[next].group = group_num;
						//cout << next << " is group " << person[next].group << endl;
						move.push(next);
					}
				}
				move.pop();
			}
		}

		if(person[a].group == person[b].group){
			cout << "yes" << endl;
		} else {
			cout << "no" << endl;
		}
	} else if(person[a].group == person[b].group){
		cout << "yes" << endl;
	} else {
		cout << "no" << endl;
	}
}

int main(){
	cin >> N >> M;
	for(int i = 0; i < N; i++)
		person[i].group = -1;
	while(M--){
		int a, b;
		cin >> a >> b;
		person[a].fr.push(b);
		person[b].fr.push(a);
	}
	cin >> Q;
	while(Q--){
		int a, b;
		cin >> a >> b;
		isFriend(a, b);
	}
	return 0;
}