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<iostream>
using namespace std;
#include<stdio.h>

typedef struct box { int val; box *prev, *next; } box_t;

box_t* init()
{
    box_t* head = new box_t;
    head->val = -1;
    head->next = NULL;
    head->prev = NULL;
    return head;
}

box_t* make_tail(box_t* head)
{
    box_t* tail = new box_t;
    tail->val = -1;
    head->next = tail;
    tail->next = NULL;
    tail->prev = head;
    return tail;
}

bool isEmpty(box_t* head, box_t* tail)
{
    return (head->next == tail ? true : false);
}

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[100000][1000];
    int dist[100000];

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes\n"); }else{ printf("no\n"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

    return 0;
}

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

int n, m, q;
vector<int> graph[100000];
vector<pair<int, int> > question;
int INF = -1;
// 未探索はINF
int group[100000];

void dfs(int i, int c) {
  group[i] = c;
  vector<int> v = graph[i];
  for (int j = 0; j < v.size(); j++) {
    if (group[v[j]] == INF) {
      dfs(v[j], c);
    }
  }
}

int main() {

  cin >> n >> m;

  // 配列を初期化
  for(int i = 0; i < n; i++) {
    group[i] = INF;
  }

  // 入力を受け取る
  for(int i = 0; i < m; i++) {
    int s, t;
    cin >> s >> t;
    graph[s].push_back(t);
    graph[t].push_back(s);
  }
  cin >> q;
  for (int i = 0; i < q; i++) {
    int s, t;
    cin >> s >> t;
    question.push_back(make_pair(s,t));
  }

  // 探索
  int id = 1;

  for (int i = 0; i < n; i++) {
    if (group[i] == INF) {
      dfs(i, ++id);
    }
  }

  // 探索結果を出力
  for (int i = 0; i < q; i++) {
    int s = question[i].first;
    int t = question[i].second;
    if (group[s] == group[t]) {
      cout << "yes" << endl;
    } else{
      cout << "no" << endl;
    }
  }

  return 0;

}

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

void set_color(const vector<vector<int> >& G, vector<int>& color,
                int color_name, int a, int i) {
    if (i >= G[a].size()) return;
    if (color[G[a][i]] == -1) {
        color[G[a][i]] = color_name;
        set_color(G, color, color_name, G[a][i], 0);
    }
    set_color(G, color, color_name, a, i + 1);
}


bool DFS(const vector<vector<int> >& G, int a, int b) {
    if (G[a].size() == 0 || G[b].size() == 0) return false;
    static vector<int> color(G.size(), -1);
    static int color_name = 0;
    if (color[a] != color[b]) return false;
    if (color[a] == -1) {
        set_color(G, color, color_name++, a, 0);
    }
    if (color[a] == color[b]) return true;
    return false;
}


int main(){
    int n, m;
    cin >> n >> m;

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

    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (vector<int>::iterator it = G[i].begin(); it != G[i].end(); it++){
//         cout << *it << " ";
//     }
//     cout << endl;
// }

    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        if (DFS(G, a, b)) {
           cout << "yes" << endl;
        } else {
           cout << "no"  << endl;
        }
    }
    return 0;
}