Go: package main

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

const MaxNode int = 1e5

var graph [][] int
var color []int
var N int

func bfs(u, c int) {
	l := list.New()
	l.PushBack(u)
	for ;l.Len()!=0; {
		u = l.Front().Value.(int)
		color[u] = c
		l.Remove(l.Front())
		for i:=0; i<len(graph[u]); i++ {
			if color[graph[u][i]] == 0 {
				l.PushBack(graph[u][i])
			}
		}
	}
}

func assignColor() {
	id := 1
	for u:=0; u<N; u++ {
		if color[u] == 0 {
			bfs(u, id)
			id ++
		}
	}
}

func nextInt(scanner *bufio.Scanner) int {
	scanner.Scan()
	num, _ := strconv.Atoi(scanner.Text())
	return num
}


func buildGraph(scanner *bufio.Scanner) {
	N = nextInt(scanner)
	color = make([]int, N)
	graph = make([][]int, N)
	m := nextInt(scanner)
	for i:=0; i<m; i++ {
		n1 := nextInt(scanner)
		n2 := nextInt(scanner)
		graph[n1] = append(graph[n1], n2)
		graph[n2] = append(graph[n2], n1)
	}
}

func answer(scanner *bufio.Scanner) {
	var outBuffer bytes.Buffer
	cnt := nextInt(scanner)
	for i:=0; i<cnt; i++ {
		n1 := nextInt(scanner)
		n2 := nextInt(scanner)
		if color[n1] == color[n2] {
			outBuffer.WriteString("yes\n")
		} else {
			outBuffer.WriteString("no\n")
		}
	}
	fmt.Printf("%s", outBuffer.String())
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	buildGraph(scanner)
	assignColor()
	answer(scanner)
}

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;
}