Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

//util
var sc = bufio.NewScanner(os.Stdin)

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

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	color         [MAX]int
)

func dfs(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			dfs(i, id)
		}
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)

	}
	assignColor()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

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


int n;

string *color = new string[n];

int *d = new int[n];

queue<int> q;

int *ans = new int[n];

vector<int> g[10000];

int i = 0;



//int c[100][100];
/*
void bfs(int x){
  color[0] = "gray";
  d[0] = 0;

  q.push(0);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int v = 0; v < n; v++){
      if(c[u][v] == 1 && color[v] == "white"){
        color[v] = "gray";
        d[v] = d[u] + 1;
        q.push(v);
      }

    }

    color[u] = "black";
    ans[i++] = x;

  }
}
*/

void bfs(int x){
  color[x] = "gray";
  q.push(x);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int i = 0; i < g[u].size(); i++){
      int v = g[u][i];
      color[v] = "gray";
      q.push(v);

    }

    color[u] = "black";
    for(int i = 0; i < n; i++){
      if(color[i] == "black"){
        ans[i] = x;
      }
    }

  }
}


int main(){

  cin >> n;

  color = new string[n];

  d = new int[n];


  /*for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      c[i][j] = 0;
    }
  }

  for(int i = 0; i < n; i++){
    int x;
    cin >> x;
    int k;
    cin >> k;
    for(int j = 0; j < k; j++){
      int v;
      cin >> v;
      c[i][v - 1] = 1;
    }
  }*/

  int m;

  cin >> m;

  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++){
    color[i] = "white";
  }




  for(int i = 0; i < n; i++){
    if(color[i] == "white"){
      bfs(i);
    }
  }

  int q;

  cin >> q;

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






  return 0;
}

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

bool search(vector<int> member,int x){
  for(int i=0; i<member.size(); i++){
    if(member[i] == x)
      return true;
  }
    return false;
}
vector<int> update(vector<int> mother,vector<int> children,int join[],int a,int b){
  mother.push_back(b);
  join[b] = join[a];
  for(int i=0; i<children.size(); i++){
    int num=children[i];
    mother.push_back(num);
    join[num] = join[a];
  }

  return mother;
}
int main(){
  int n,m,join[10000],s,t;
  vector<int> group[10000];
  cin >> n >> m;

  for(int i=0; i<n; i++)
    join[i] = i;
    
  for(int i=0; i<m; i++){
    cin >> s >> t;
    bool flag = search(group[join[t]],s);

    if(!flag){
      int x = join[t];

      if(x!=t || !group[x].empty())
	group[x] = update(group[x],group[s],join,x,s);


      else{
	group[join[s]].push_back(t);
	join[x] = join[s];
      }
    }

  }
 
  int q;
  cin >> q;
  
  bool answer[10000];
  for(int i=0; i<q; i++){
    cin >> s >> t;
    
    if(join[s] == join[t])
      answer[i]=true;
    else
      answer[i]=false;
  }

  for(int i=0; i<q; i++){
    if(answer[i])
      cout << "yes\n";
    else
      cout << "no\n";
  }
}

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

#include <memory>
#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
*/

const int kMaxUsers = 100 * 1000;

bool g_isVisited[kMaxUsers]; // 100 KiB
multimap<int, int> g_relations; // 800 KiB at least
multimap<int, int> g_reachable; // 800 KiB at least


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


void setReachable(int start, int end)
{
  g_reachable.insert(make_pair(start, end));
}


bool checkReachableFromStatic(int start, int end)
{
  g_reachable.insert(make_pair(start, end));

  std::multimap<int, int>::iterator it;
  for (it = g_reachable.equal_range(start).first; it != g_relations.equal_range(start).second; it++)
  {
    if (it->second == end)
      return true;
  }

  return false;
}


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

  // init
  memset(g_isVisited, 0, num);

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

  while (!que.empty())
  {
    int id = que.front();

    if (checkReachableFromStatic(id, end))
      return string("yes");

    que.pop();
    g_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)
      {
        setReachable(start, end);
        return string("yes");
      }

      if (!g_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;

}