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 <iostream>
#include <vector>
#include <set>

using namespace std;

vector<set<int>> A;


bool dfs(int s, int t) {
    auto& S = A[s];
    if (S.find(t) != S.end()) {
        return true;
    }
    for (auto it = S.begin(); it != S.end(); ++it) {
        if (*it != t) {
            if (dfs(*it, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int n;
    int m;
    cin >> n >> m;
    A.resize(n);
    for (int i = 0; i < m; ++i) {
        int s, t;
        if (s > t) {
            swap(s, t);
        }
        cin >> s >> t;
        A[s].insert(t);
        // A[t].insert(s);
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

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

bool dfs(int node, int gole, vector<vector<int> >& adjlist, vector<bool>& used){

    if(node == gole) return true;

    for(int i = 0; i < adjlist[node].size(); i++){
        if(used[adjlist[node][i]] == false){
            used[adjlist[node][i]] = true;
            bool flag = dfs(adjlist[node][i], gole, adjlist, used);
            if(flag) return true;
        }
    }

    return false;
}

int main(){

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

    vector<vector<int> > adjlist(n);               

    //入力
    for(int i = 0; i < m; i++){
        int a, b; cin >> a >> b;                   // a ←→ b に辺がある
        adjlist[a].push_back(b);
        adjlist[b].push_back(a);
        
    }

    //質問
    int q; cin >> q;
    for(int i = 0; i < q; i++){
        int a, b; cin >> a >> b;
        
        vector<bool> used(n, false);
        used[a] = true;
        if(dfs(a, b, adjlist, used)) cout << "yes" << endl;
        else cout << "no" << endl;
    }

    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <climits>
#include <string>
#include <vector>
#include <utility>
#include <functional>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cassert>

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const ll MOD = ll(1e9) + 7;
const ll INF = LLONG_MAX;
const ll MAX_N = ll(1e5) + 5;
const double EPS = 10e-8;
const double PI = 3.14159265359;

#define REP(i, n) for (ll i = 0; i < n; i++)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOR(i, m, n) for (ll i = m; i < n; i++)

int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};

struct UF{
    static const int MAX_N = 100000;
    int p[MAX_N];
    int r[MAX_N];

    void init(int n){
        REP(i,n){
            p[i]=i;
            r[i]=0;
        }
    }
    int find(int x){
        if(p[x]==x)return x;
        return p[x] = find(p[x]);
    }
    void unite(int x, int y){
        x = find(x);
        y = find(y);
        if(x == y)return;
        if(r[x] < r[y])swap(x,y);
        if(r[x]==r[y])r[x]++;
        p[y]=x;
    }
    bool same(int x, int y){
        return find(x)==find(y);
    }
};

int main() {
    int n,m,q;
    cin >> n >> m;
    UF g;
    g.init(n);
    REP(i,m){
        int a,b;
        cin >> a >> b;
        g.unite(a,b);
    }
    cin >> q;
    REP(i,q){
        int a,b;
        cin >> a >> b;
        if(g.same(a,b))cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include <cstdio>
#include <algorithm>
#include <unordered_set>
#include <vector>

int main(){
    int n;
    int m;
    std::scanf("%d", &n);
    std::scanf("%d", &m);
    std::vector<std::unordered_set<int> > relations;
    for(int i = 0; i < m; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        int finds = -1;
        int findt = -1;
        for(int j = 0; j < relations.size(); ++j){
            if(relations[j].find(s) != relations[j].end()){
                finds = j;
            }
            if(relations[j].find(t) != relations[j].end()){
                findt = j;
            }
            if(findt != -1 && finds != -1) break;
        }
        for(int j = 0; j < relations.size(); ++j){
        }
        if(finds == -1 && findt == -1){
            std::unordered_set<int> set;
            set.insert(s);
            set.insert(t);
            relations.push_back(set);
        } else if(findt == -1){
            relations[finds].insert(t);
        } else if(finds == -1){
            relations[findt].insert(s);
        } else if(finds != findt){

            int smaller = (relations[finds].size() < relations[findt].size()) ? finds : findt;
            int larger = (smaller == findt) ? finds : findt;
            for(auto &x: relations[smaller]){
                relations[larger].insert(x);
            }
            relations[smaller] = relations.back();
            relations.pop_back();
        }
    }
    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);
        bool find = false;
        for(int j = 0; j < relations.size(); ++j){
            if(relations[j].find(s) != relations[j].end() && relations[j].find(t) != relations[j].end()){
                find = true;
		break;
            }
        }
        if(find){
            std::printf("yes\n");
        } else {
            std::printf("no\n");
        }
    }

    return 0;
}