Go: package main

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

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	for i := 0; i < n; i++ {
		group[i] = i
	}
	
	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())

		if group[s] < group[t] {
			group[t] = group[s]
		} else {
			group[s] = group[t]
		}
	}

	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 root(s, &group) == root(t, &group) {
			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<vector>
#include<limits.h>
#include<stack>
#include<string>
using namespace std;

vector< vector<int> > L(100005);
int c[100005]={};

void dfs (int v, int marker){
	if(c[v]!=0){
		return;
	}
	c[v]=marker;
	for (int i=0;i<L[v].size();i++){
		dfs(L[v][i],marker);
	}
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	int n,m,a,b,q,s,t;
	cin >> n >> m;
	
	for (int i=0;i<m;i++){
		cin >> a >> b;
		L[a].push_back(b);
	}
	
	int marker=1;
	for (int i=0;i<n;i++){
		if (c[i]==0){
			dfs(i,marker);
			marker++;
		}
	}
	
	
	cin >> q;
	int d[2][q];
	for (int i=0;i<q;i++){
		cin >> d[i][0];
		cin >> d[i][1]; 
	}
	for (int i=0;i<q;i++){
		if(c[d[i][0]]==c[d[i][1]]){
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}
	return 0;
}

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

struct node {
	int parent;
	std::vector<int> relation;
};

void dfs(std::vector<node> &n) {
	int d[100000];

	std::stack<int> s;
	for (size_t i = 0; i < n.size(); i++) {
		s.push(i);
		for (int k = 0; k < 100000; k++) {
			d[k] = 0;
		}
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			for (std::vector<int>::iterator it = n[num].relation.begin(); it != n[num].relation.end(); it++) {
				if (d[*it] == 1) {
					n[num].relation.erase(it);
					it--;
				} else {
					s.push(*it);
					d[*it] = 1;
				}
			}
		}
	}
}

void makeparent(std::vector<node> &n) {
	std::queue<int> q;
	for (size_t i = 0; i < n.size(); i++) {
		n[i].parent = -1;
	}
	for (size_t i = 0; i < n.size(); i++) {
		q.push(i);
		int parent = i;
		while (q.size() != 0) {
			parent = q.front(); q.pop();
			for (size_t j = 0; j < n[parent].relation.size(); j++) {
				q.push(n[parent].relation[j]);
				n[n[parent].relation[j]].parent = parent;
			}
		}
	}
}

bool isconnect(std::vector<node> n, int from, int to) {
	std::stack<int> s;
	while (n[from].parent != -1) {
		from = n[from].parent;
	}
	if (to == from) return true;
	s.push(from);
	while(s.size() != 0) {
		from = s.top(); s.pop();
		for (std::vector<int>::iterator it = n[from].relation.begin(); it != n[from].relation.end(); it++) {
			if (to == *it) return true;
			s.push(*it);
		}
	}
	return false;
}

int main() {
	int people, relation;
	
	std::cin >> people >> relation;

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

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

	dfs(n);
	makeparent(n);

	/*
	for (size_t i = 0; i < n.size(); i++) {
		std::cout << i << " " << n[i].parent << std::endl;
	}

	for (size_t i = 0; i < n.size(); i++) {
		for (size_t j = 0; j < n[i].relation.size(); j++) {
			std::cout << i << n[i].relation[j] << std::endl;
		}
	}
	*/

	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		if (isconnect(n, from, to)) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
#define N 100000

int group[N];
vector<int> vec[N];
int n,m;

int dfs_visit(int x,int k){
  stack<int> S;
  S.push(x);
  while(!S.empty()){
    int u=S.top();S.pop();
    for(int i=0;i<vec[u].size();i++){
      int v=vec[u][i];
      if(group[v]==0){
        group[v]=k;
        S.push(v);
      }
    }
  }
}
void dfs(){
  int id=1;
  for(int i=0;i<n;i++){
    if(group[i]==0) dfs_visit(i,id++);
  }
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
    int s,t;
    cin>>s>>t;
    vec[s].push_back(t);
    vec[t].push_back(s);
  }
  dfs();
  int q;
  cin>>q;
  for(int i=0;i<q;i++){
    int a,b;
    cin>>a>>b;
    if((group[a]!=0&&group[b]!=0)&&group[a]==group[b]){
      cout<<"yes"<<"\n";
    }else{
      cout<<"no"<<"\n";
    }
  }
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>
#include <set>
#include <list>
#include <cstring>
#include <stack>

using namespace std;

#define mod 1000000007

class UF
{
private:
	vector<int> root;

public:
	UF(int n)
	{
		root = vector<int>(n + 1, -1);
	}

	int getroot(int n)
	{
		if(root[n] == -1) return n;
		else return root[n] = getroot(root[n]);
	}

	void add(int x, int y)
	{
		x = getroot(x);
		y = getroot(y);
		if(x == y) return;
		if(x > y) swap(x, y);
		root[y] = x;
		return;
	}
};

int main()
{
	int n, m;
	cin >> n >> m;
	UF uf(n);
	for(int i = 0; i < m; i++){
		int s, t;
		cin >> s >> t;
		uf.add(s, t);
	}
	int q;
	cin >> q;
	for(int i = 0; i < q; i++){
		int s, t;
		cin >> s >> t;
		if(uf.getroot(s) == uf.getroot(t)) cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <algorithm>
#include <unordered_map>
#include <vector>
int main(){
    int n;
    int m;
    std::scanf("%d", &n);
    std::scanf("%d", &m);

    std::unordered_map<int, int> map;
    for(int i = 0; i < m; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        if(map.find(s) == map.end() && map.find(t) == map.end()){
            int small = std::min(s, t);
            int large = std::max(s, t);
            map.insert(std::make_pair(small, small));
            map.insert(std::make_pair(large, small));
        } else if(map.find(s) == map.end()){
            int key = map[t];
            while(key != map[key]){
                key = map[key];
            }
            if(key <= s){
                map.insert(std::make_pair(s, key));
            } else {
                map[key] = s;
                map.insert(std::make_pair(s, s));
            }
        } else if(map.find(t) == map.end()){
            int key = map[s];
            while(key != map[key]){
                key = map[key];
            }
            if(key <= t){
                map.insert(std::make_pair(t, key));
            } else {
                map[key] = t;
                map.insert(std::make_pair(t, t));
            }
        } else {
            int keys = map[s];
            while(keys != map[keys]){
                keys = map[keys];
            }
            int keyt = map[t];
            while(keyt != map[keyt]){
                keyt = map[keyt];
            }
            int small = std::min(keys, keyt);
            int large = std::max(keys, keyt);
            map[large] = small;
        }
    }
    int q;
    std::scanf("%d", &q);
    for(int i = 0; i < q; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);

	int keys = map[s];
        while(keys != map[keys]){
            keys = map[keys];
        }
        int keyt = map[t];
        while(keyt != map[keyt]){
            keyt = map[keyt];
        }
        if(keys == keyt){
            std::printf("yes\n");
        } else {
            std::printf("no\n");
        }
    }

    return 0;
}