Go: package main

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

const MAX = 100000

type Queue struct {
	head      int
	tail      int
	container [MAX]int
}

func (q *Queue) push(n int) {
	q.container[q.tail] = n
	q.tail = (q.tail + 1) % MAX
}

func (q *Queue) pop() int {
	res := q.container[q.head]
	q.head = (q.head + 1) % MAX
	return res
}

func (q *Queue) isEmpty() bool {
	return q.head == q.tail
}

var sc = bufio.NewScanner(os.Stdin)
var route [][]int
var SEEN [MAX]bool
var GROUP [MAX]int

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func bfs(start, group int) {
	que := Queue{}
	que.push(start)

	for !que.isEmpty() {
		id := que.pop()

		if SEEN[id] {
			continue
		}
		SEEN[id] = true
		GROUP[id] = group

		for _, next := range route[id] {
			que.push(next)
		}
	}
}

func main() {
	n, m := scanInt(), scanInt()
	route = make([][]int, n)
	for i := 0; i < m; i++ {
		s, t := scanInt(), scanInt()
		route[s] = append(route[s], t)
		route[t] = append(route[t], s)
	}

	for i := 0; i < n; i++ {
		if !SEEN[i] {
			bfs(i, i+1)
		}
	}

	w := bufio.NewWriter(os.Stdout)
	q := scanInt()
	for i := 0; i < q; i++ {
		s, t := scanInt(), scanInt()
		if GROUP[s] == GROUP[t] {
			fmt.Fprintln(w, "yes")
		} else {
			fmt.Fprintln(w, "no")
		}
	}
	w.Flush()
}

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

void dfs(int root, int node, vector<vector<int> >& adjlist, vector<int>& used){

    for(int i = 0; i < adjlist[node].size(); i++){
        if(used[adjlist[node][i]] == -1){
            used[adjlist[node][i]] = root;
            dfs(root, adjlist[node][i], adjlist, used);
        }
    }
}

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);
        
    }

    vector<int> used(n, -1);

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

    /*for(int i = 0; i < n; i++){
        cout << i << " " << used[i] << endl;
    }*/

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

    return 0;
}

C++: #include <map>
#include <set>
#include <list>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <utility>
#include <iostream>
#include <algorithm>
#include <functional>
#include <unordered_map>
#include <unordered_set>

using namespace std;

#define ll long long
#define ull unsigned long long
#define INF (1 << 30)
#define LLINF (1LL << 62)
#define MOD7 1000000007
#define MOD9 1000000009
#define eps 1e-9
#define P pair<int, int>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pul pair<ull, ull>
#define all(a) (a).begin(), (a).end()
#define FOR(i,a,b) for (int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);--i)
#define REP(i,n) for (int i=0;i<(n);++i)
#define RREP(i,n) for (int i=(n)-1;i>=0;--i)

void YES() { cout << "YES" << endl; }
void NO() { cout << "NO" << endl; }
void Yes() { cout << "Yes" << endl; }
void No() { cout << "No" << endl; }
void yes() { cout << "yes" << endl; }
void no() { cout << "no" << endl; }

template<class T>
class UnDirectedGraph {
public:
	class Edge {
	public:
		int to;
		T cost;

		Edge(int t, T c) : to(t), cost(c) {}

		bool operator<(const Edge& right) const {
			return cost == right.cost ? to < right.to : cost < right.cost;
		}
	};

	vector<vector<Edge>> G;
	int V;

	UnDirectedGraph(int n = 0) {
		resize(n);
	}

	void resize(int n) {
		V = n;
		G.resize(n);
	}

	void addEdge(int from, int to, T cost = 0) {
		int v = max(from, to);
		if (v >= V)
			resize(v + 1);
		G[from].push_back(Edge(to, cost));
		G[to].push_back(Edge(from, cost));
	}

	vector<int> visit;
	int col = 0;
	void dfs(int s) {
		//vector<int> visit(V);
		visit.resize(V);
		col++;
		calcDfs(visit, s);
	}

	void calcDfs(vector<int>& visit, int s) {
		if (visit[s])
			return;

		//visit[s] = 1;
		visit[s] = col;
		for (int i = 0; i < G[s].size(); ++i) {
			calcDfs(visit, G[s][i].to);
		}
	}

	vector<int> bfs(int s) {
		vector<int> dist(V);
		queue<int> que;

		fill(dist.begin(), dist.end(), -1);
		dist[s] = 0;
		que.push(s);
		while (!que.empty()) {
			int from = que.front();
			que.pop();
			for (int i = 0; i < G[from].size(); ++i) {
				int to = G[from][i].to;
				if (dist[to] != -1)
					continue;
				dist[to] = dist[from] + 1;
				que.push(to);
			}
		}

		return dist;
	}
};

int main() {
	int n, m, from, to;
	cin >> n >> m;
	UnDirectedGraph<int> g(n);
	while (m--) {
		cin >> from >> to;
		g.addEdge(from, to);
	}
	
	for (int i = 0; i < n; ++i)
		g.dfs(i);

	int q;
	cin >> q;
	while (q--) {
		cin >> from >> to;
		if (g.visit[from] == g.visit[to])
			yes();
		else
			no();
	}

	return 0;
}

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

using namespace std;

#define Vi vector<int>
#define FOR(i,s,e) for (int i=s; i<e; i++)
#define ITER(v) v.begin(), v.end()

constexpr int N_MAX = 100'000;

Vi adj[N_MAX];

int n;
bool isconnected(const int a, const int b) {
    bool isqueued[N_MAX] = {false};
    queue<int> q;
    q.push(a);
    isqueued[a] = true;
    while (!q.empty()) {
        const int i = q.front();
        //cout << "#" << i << endl;
        if (i == b) { return true; }
        for (const int j : adj[i]) {
            if (isqueued[j]) { continue; }
            q.push(j);
            isqueued[j] = true;
        }
        q.pop();
    }
    return false;
}

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

    int m;
    cin >> n >> m;

    int a, b;
    FOR(i,0,m) {
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    /*
    cout << "adj read." << endl;
    FOR(i,0,n) {
        for (const int j : adj[i]) {
            cout << " " << j;
        }
        cout << endl;
    }
    */

    int q;
    cin >> q;
    FOR(i,0,q) {
        cin >> a >> b;
        cout << (isconnected(a, b) ? "yes" : "no") << endl;
    }

    return 0;
}