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 <cstdio>
#include <vector>
#include <cstring>
#include <cstdlib>

void numbering(int id, int *g, int num, std::vector<int> *a){
    int tmp;
    for(int i=0;i<a[id].size();i++){
        tmp = a[id][i];
        if(g[tmp])continue;
        g[tmp] = num;
        numbering(tmp, g, num, a);
    }
}

void grouping(std::vector<int> *a, int *g, int n){
    int num = 1;
    for(int i=0;i<n;i++){
        if(g[i])continue;
        g[num] = num;
        numbering(i,g,num,a);
        num++;
    }
}

int main(){
    int i, n, m, q, s, t;
    int *g;
    scanf("%d %d",&n,&m);
    g = (int *)malloc(sizeof(int)*n);
    memset(g, 0, sizeof(int)*n);
    std::vector<int> a[n];
    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        a[s].push_back(t);
        a[t].push_back(s);
    }
    scanf("%d",&q);
    grouping(a,g,n);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(g[s]==g[t])printf("yes\n");
        else printf("no\n");
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define rep(i,N) for(ll i=0;i<N;++i)
typedef long long int ll;
ll INF = 1LL<<60;

ll n,m;

struct UnionFind {
  vector< int > data;
 
  UnionFind(int sz) {
    data.assign(sz, -1);
  }
 
  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if(x == y) return (false);
    if(data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return (true);
  }
 
  int find(int k) {
    if(data[k] < 0) return (k);
    return (data[k] = find(data[k]));
  }
 
  int size(int k) {
    return (-data[find(k)]);
  }
};

int main(){
    cin >> n >> m;
    UnionFind tree(n);
    rep(i,m){
        int x,y; cin >> x >> y;
        tree.unite(x,y);
    }
    int q; cin >> q;
    rep(i,q){
        int x,y; cin >> x >> y;
        if(tree.find(x) != -1 && tree.find(y) != -1){
            if(tree.find(x) == tree.find(y)) cout << "yes" << endl;
            else cout << "no" << endl;
        }else cout << "no" << endl;
    }
}

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[4000][50];
    int *dist;

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

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);

	dist = new int [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);
    }

	delete [] dist;

    return 0;
}

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

const long N = 100;
const long WHITE = 0;
const long GRAY = 1;
const long BLACK = 2;

long n, M[N + 1][N + 1];
long color[N + 1], cc[N + 1], cp = 0;
long nt[N + 1];

long next(long u){
	for (long v = nt[u]; v <= n; v++){
		nt[u] = v + 1;
		if (M[u][v]) return v;
	}
	return -1;
}

void dfs_visit(long r){
	for (long i = 1; i <= n; i++) nt[i] = 1;

	stack<long> S;
	S.push(r);
	color[r] = GRAY;

	while (!S.empty()){
		long u = S.top();
		long v = next(u);
		if (v != -1){
			if (color[v] == WHITE){
				color[v] = GRAY;
				S.push(v);
			}
		}
		else {
			S.pop();
			color[u] = BLACK;
			cc[u] = cp;
		}
	}
}

void dfs(){
	for (long i = 1; i <= n; i++){
		color[i] = WHITE;
		nt[i] = 1;
	}

	for (long u = 1; u <= n; u++){
		if (color[u] == WHITE){
			dfs_visit(u);
			cp++;
		}
	}

}

int main(){
	long m, q;
	cin >> n >> m;
	for (long i = 1; i <= n; i++){
		for (long j = 1; j <= n; j++){
			M[i][j] = 0;
		}
	}
	for (long i = 0; i < m; i++){
		long s, t;
		cin >> s >> t;
		M[s][t] = 1;
	}
	dfs();
	cin >> q;
	for (long i = 0; i < q; i++){
		long s, t;
		cin >> s >> t;
		if (cc[s] == cc[t]) cout << "yes" << endl;
		else cout << "no" << endl;
	}

	return 0;
}