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

#include <cstring>
#include <queue>
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


const int kInvalid = -1;
const int kMaxUsers = 100 * 1000 + 1;

int g_group[kMaxUsers]; // 400 KiB

// 100 K * sizeof(vector<int>) + 100 K * sizeof(int)
// = 2.4 MiB + 100 K * sizeof(int)
vector<int> g_list[kMaxUsers];

void setRelations(int start, int end)
{
  g_list[start].push_back(end);
  g_list[end].push_back(start);
}


void doGrouptize()
{
  // debug info
  DPRINTF("size of g_group[] %lu Byte\n", sizeof(g_group));
  DPRINTF("size of g_list[]  %lu Byte\n", sizeof(g_list));

  // init
  int groupId = 0;
  //memset(g_group, kInvalid, kMaxUsers);
  for (int i = 0; i < kMaxUsers; i++)
    g_group[i] = kInvalid;

  for (int i = 0; i < kMaxUsers; i++)
  {
    if (g_group[i] != kInvalid)
      continue;

    g_group[i] = groupId;

    // grouptize connected users in BFS order
    queue<int> que;
    que.push(i);

    while (!que.empty())
    {
      const int current = que.front();
      que.pop();

      for (int j = 0; j < g_list[current].size(); j++)
      {
        const int next = g_list[current][j];

        if (g_group[next] != kInvalid)
          continue;

        g_group[next] = groupId;
        que.push(next);
      }
    }

    groupId++;
  }
}


void printAllRelations()
{
#if DEBUG
  for (int i = 0; i < kMaxUsers; i++)
  {
    for (int j = 0; j < g_list[i].size(); j++)
    {
      if (j == 0)
        DPRINTF("%d", i);

      printf(" %d", g_list[i][j]);

      if (j == g_list[i].size() - 1)
        cout << endl;
    }
  }
#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();

  doGrouptize();

  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);

    if (g_group[s] == g_group[t])
      cout << "yes" << endl;
    else
      cout << "no" << endl;
  }

  return 0;

}

C++: #include <iostream>
#include <vector>
#include <cmath>
#include <queue>


std::vector<int> V[100000];
int C[100000];
int color;
int maxi;

int main () {
    int n, m, q;
    std::cin >> n >> m;

    for (int i; i < m; i++) {
        int s, t;
        std::cin >> s >> t;
        V[s].push_back(t);
        V[t].push_back(s);
    }

    for (int i = 0; i < n; i++) {
        if(C[i] == 0) {
            color++;
            std::queue<int> Q;
            Q.push(i);
            while (Q.size()) {
                C[Q.front()] = color;
                for (auto t: V[Q.front()]) {
                    if (C[t] == 0) {
                        C[t] = color;
                        Q.push(t);
                    }
                }
                Q.pop();
            }
        }
    }

    std::cin >> q;
    for (int i = 0; i < q; i++) {
        int s, t;
        std::cin >> s >> t;
        if ((C[s] == C[t]) && (C[s] != 0)) {
            std::cout << "yes" << std::endl;
        }
        else{
            std::cout << "no" << std::endl;
        }
    }

}

C++: #include <iostream>
#include<stack>
#include<queue>
using namespace std;
const int MAXn=100000;
const int NIL=-1;

int n,col[MAXn];
vector<int> G[MAXn];

void dfs(int r,int c)
{
	stack<int> S;
	S.push(r);
	col[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(col[v]==NIL)
			{
				col[v]=c;
				S.push(v);
			}
		}
	}
	return;
}

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

int main() {
	int m,a,b,q;cin>>n>>m;
	for(int i=0;i<m;i++)
	{
		cin>>a>>b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	assigncol();
	cin>>q;
	for(int i=0;i<q;i++)
	{
		cin>>a>>b;
		if(col[a]==col[b])cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}