Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

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

#define rep(i, a, b) for (int i = a; i < (int)(b); ++i)
#define rrep(i, a, b) for (int i = b - 1; i >= (int)(a); --i)

using namespace std;

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;

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

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

    vvi g(n);

    rep(i, 0, m) {
        int s, t;
        cin >> s >> t;

        g[s].push_back(t);
        g[t].push_back(s);
    }

    vi map(n, -1);
    vector<bool> seen(n, false);

    int t = 0;
    rep(i, 0, n) {
        if (seen[i]) { continue; }
        queue<int> st;
        st.push(i);
        seen[i] = true;
        map[i] = t;

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

            for (auto itr = g[v].begin(); itr != g[v].end(); ++itr) {
                if (!seen[*itr]) {
                    st.push(*itr);
                    seen[*itr] = true;
                    map[*itr] = t;
                }
            }
        }
        ++t;
    }

    cin >> q;
    rep(i, 0, q) {
        int s, t;
        cin >> s >> t;
        cout << (map[s] == map[t] ? "yes" : "no") << endl;
    }

    return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <list>
#include <string>
#include <vector>

class TUser
{
	std::list<TUser*> FAccessible;
public:
	void AddFriend(TUser* Friend);
	bool IsAccesible(const TUser* Target)const;
};

void TUser::AddFriend(TUser* Friend)
{
	if(IsAccesible(Friend)) return;
	FAccessible.push_back(Friend);
	for(std::list<TUser*>::iterator It = FAccessible.begin(); It != FAccessible.end(); ++It){
		(*It)->AddFriend(Friend);
		Friend->AddFriend(*It);
	}
}

bool TUser::IsAccesible(const TUser* Target)const
{
	return std::find(FAccessible.begin(), FAccessible.end(), Target) != FAccessible.end();
}

class TSns
{
	std::vector<TUser> FUsers;
public:
	TSns(int UserCount);
	
	void AddLink(int UserA, int UserB);
	std::string IsAccesible(int UserA, int UserB)const;
};

TSns::TSns(int UserCount)
: FUsers(UserCount)
{
}

void TSns::AddLink(int UserA, int UserB)
{
	FUsers[UserA].AddFriend(&FUsers[UserB]);
	FUsers[UserB].AddFriend(&FUsers[UserA]);
}

std::string TSns::IsAccesible(int UserA, int UserB)const
{
	if(FUsers[UserA].IsAccesible(&FUsers[UserB]) || FUsers[UserB].IsAccesible(&FUsers[UserA])) return "yes";
	return "no";
}

int main()
{
	int UserCount;
	std::cin >> UserCount;
	TSns Sns(UserCount);
	
	int LinkCount;
	std::cin >> LinkCount;
	for(int i = 0; i < LinkCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		Sns.AddLink(UserA, UserB);
	}
	
	int QuestionCount;
	std::cin >> QuestionCount;
	for(int i = 0; i < QuestionCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		std::cout << Sns.IsAccesible(UserA, UserB) << std::endl;
	}
	return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;
using v1 = vector<int>;
using vl = vector<long long>;
using v2 = vector<vector<int>>;
using v3 = vector<vector<char>>;

int N;
vector<int> G[100000];
int color[100000];

void dfs(int s, int c){
	stack<int> S;
	S.push(s);
	color[s] = c;
	while(!S.empty()){
		int u = S.top();
		S.pop();
		rep(i, G[u].size()){
			int p = G[u][i];
			if(color[p] == 0){
				color[p] = c;
				S.push(p);
			}
		}
	}
}

void colorAssign(){
	rep(i, N){
		color[i] = 0;
	}
	int id = 1;
	rep(i, N){
		if(color[i] == 0){
			dfs(i, id);
			id++;
		}
	}

}

int main(){
	int m, s, t;
	cin >> N >> m;
	rep(i, m){
		cin >> s >> t;
		G[s].push_back(t);
		G[t].push_back(s);
	}
	colorAssign();
	int q;
	cin >> q;
	rep(i, q){
		cin >> s >> t;
		if(color[s] == color[t]) cout << "yes" << endl;
		else cout << "no" << endl;
	}
}

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

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

void dfs(std::vector<node> &n) {
	std::stack<int> s;
	std::vector<int> d(n.size()), dd(n.size());
	for (size_t i = 0; i < n.size(); i++) {
		std::fill(d.begin(), d.end(), 0);
		s.push(i);
		if (dd[i] == 1)continue;
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			dd[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;
					std::vector<int>::iterator itt= std::find(n[*it].relation.begin(), n[*it].relation.end(), num);
					if (itt != n[*it].relation.end()) {
						n[*it].relation.erase(itt);
					}
				}
			}
		}
	}
}

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 (from == to) 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;
}