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 <stdio.h>
#include <stdint.h>
#include <iostream>
#include <fstream>
#include <cassert>
#include <climits>

#include <queue>
#include <map>
#include <utility>
using namespace std;

#define DEBUG (0)

#if DEBUG
#define DPRINTF(...) do { \
    printf("D(L%d) %s: ", __LINE__, __func__); \
    printf(__VA_ARGS__); \
  } while (false)
#else
#define DPRINTF(...)
#endif // DEBUG

/*
   Memory limitaion; 64 MiB
   # of users: 2 <= n <= 100 K
   # of relations: 0 <= m <= 100 K

   Data size:
    1) for relations (maybe hash table):
      100K * 4Byte * 2 (bi-direction) = 800K

    2) for visited flag:
      100K * 1Byte = 100K
*/

multimap<int, int> g_relations;

void setRelations(int id0, int id1)
{
  g_relations.insert(make_pair(id0, id1));
  g_relations.insert(make_pair(id1, id0));
}


string isReachable(int num, int start, int end)
{

  bool isVisited[num];

  for (int i = 0; i < num; i++)
    isVisited[i] = false;

  queue<int> que;
  que.push(start);

  while (!que.empty())
  {
    int id = que.front();
    que.pop();
    isVisited[id] = true;

    // if no path from "id", try next
    if (g_relations.count(id) == 0)
      continue;

    // check all pathes connected from "id"
    std::multimap<int, int>::iterator it;
    for (it = g_relations.equal_range(id).first; it != g_relations.equal_range(id).second; it++)
    {
      int &dst = it->second;

      if (dst == end)
        return string("yes");

      if (!isVisited[dst])
        que.push(dst);

    }
  }

  return string("no");
}


void printAllRelations()
{
#if DEBUG
  for (auto& m: g_relations)
    DPRINTF("%d %d\n", m.first, m.second);
#endif // DEBUG
}

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

  DPRINTF("number of users %d\n", n);
  DPRINTF("number of relations %d\n", m);

  for (int i = 0; i < m; i++)
  {
    int s, t;
    cin >> s >> t; cin.ignore();

    setRelations(s, t);
  }

  printAllRelations();

  int q;
  cin >> q; cin.ignore();

  for (int i = 0; i < q; i++)
  {
    int s, t;
    cin >> s >> t; cin.ignore();

    DPRINTF("src %d  dst %d\n", s, t);

    cout << isReachable(n, s, t) << endl;
  }

  return 0;

}

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

static const int MAX =100000;
static const int NIL=-1;

int n;
vector<int> G[MAX];
int color[MAX];

void dsf(int r,int c){
  stack<int> S;
  S.push(r);
  color[r]=c;
  while(!S.empty()){
    int u=S.top();S.pop();
    for(int i=0;i<G[u].size();i++){
      int v=G[u][i];
      if(color[v]==NIL){
        color[v]=c;
        S.push(v);
      }
  }
}

void assignColor(){
  int id=1;
  for(int i=0;i<n;i++) color[i]=NIL;
  for(int u=0;u<n;u++){
    if(color[u]==NIL)dfs(u,id++);
  }
}

int main (){
  int s,t,m,q;
  cin >> n >>m;
  for(int i=0;i<m;i++){
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();
  cin >>q;
  for(int i=0;i<q;i++){
    if(color[s]==color[t]){
      cout <<"yes"<< endl;
    }else{
      cout << "no" <<endl;
    }
  }

  return 0;
}

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

static const int MAX = 100000;
static const int NIL = -1;


int n;
vector<int> G[MAX];
int color[MAX];

void dfs(int r, int c){
    static<int> S;
    S.push(r);
    color[r] = c;
    while (!S.empty()){
        int u = S.top(); S.pop();
        for(int i = 0; i < G[u].size(); i++){
            int v = G[u][i];
            if (color[v] == NIL){
                color[v] = c;
                S.push(v);
            }
        }
    }
}

void assignColor(){
    int id = 1;
    for(int i = 0; i < n; i++) color[i] = NIL;
    for(int u = 0; u < n; u++){
        if(color[u] == NIL) dfs(u, id++);
    }
}

int main(){
    int s, t, m, q;

    cin >> n >> m;

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

    assignColor();

    cin >> q;

    for(int i = 0; i < q; i++){
        cin >> s >> t;
        if(color[s] == color[t]){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }

    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int f[100001],n,m,q;
int getf(int u){
	if(u==f[u])return u;
	else return f[u]=getf(f[u]);
	}
int merge(int u,int v){
	int t1=getf(u);
	int t2=getf(v);
	if(t1!=t2){
		f[t2]=t1;
			}
}	
int main(){
	int v1,v2;
	scanf("%d%d",&n,&m);
	for(int i=0;i<n;i++)f[i]=i;
	for(int i=0;i<m;i++){
		scanf("%d%d",&v1,&v2);
		merge(v1,v2); 
	}
	scanf("%d",&q);
	for(int i=0;i<q;i++){
		scanf("%d%d",&v1,&v2);
		if(getf(v1)==getf(v2))printf("yes\n");
		else printf("no\n");
	}
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <utility>
#include <queue>
#include <stack>
#include <string>
#include <climits>
using namespace std;

#define MAX_N  100000
#define MAX_M  100000
#define MAX_Q  10000

int n, m, q;
queue<int> Q;

int bf(vector<vector<int> >& sns, int src, int dst)
{
    int d[MAX_N] = {};
    Q.push(src);
    while (!Q.empty()) {
        if (dst == (src = Q.front())) return 1;
        Q.pop();
        d[src]++;
        for (auto itr = sns.at(src).begin(); itr != sns.at(src).end(); itr++) {
            if (!d[*itr]) Q.push(*itr);
        }
    }
    return 0;
}

int main()
{
    cin >> n >> m;
    vector<vector<int> > sns(n);
    int s, d;
    while (m--) {
        cin >> s >> d;
        sns.at(s).push_back(d);
        sns.at(d).push_back(s);
    }
    cin >> q;
    while (q--) {
        cin >> s >> d;
        cout << (bf(sns, s, d) ? "yes" : "no") << endl;
    }
    return 0;
}