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 <bits/stdc++.h>
#define r(i,a,n) for(int i=a;i<n;i++)
using namespace std;
vector<int>G[100000];
queue<int>Q;
int col[100000],n,id=1;
void bfs(int u,int c){
	Q.push(u);
	col[u]=c;
	while(!Q.empty()){
		u=Q.front();Q.pop();
		r(i,0,G[u].size()){
			int w=G[u][i];
			if(col[w]==-1){
				Q.push(w);
				col[w]=c;
			}
		}
	}
}
void Color(){
	r(i,0,100000)col[i]=-1;
	r(i,0,n)if(col[i]==-1)bfs(i,id++);
}
int main(){
	int s,t,m,q;
	cin>>n>>m;
	r(i,0,m){
		cin>>s>>t;
		G[s].push_back(t);
		G[t].push_back(s);
	}
	Color();
	cin>>q;
	while(q--){
		cin>>s>>t;
		if(col[s]==col[t])cout<<"yes";
		else cout<<"no";
		cout<<endl;
	}
}

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

#include <cstring>
#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


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

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

    return 0;
}

C++: // C++ 14
#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <queue>
#include <stack>
#include <math.h>

#define ll long long
#define Int int
#define loop(x, start, end) for(Int x = start; x < end; x++)
#define loopdown(x, start, end) for(int x = start; x > end; x--)

using namespace std;

void dfs_color(vector<Int> vs[], Int colors[], Int n) {
    bool visited[n];
    loop(i,0,n)  {
        visited[i] = false;
        colors[i] = 0;
    }
    
    stack<Int> S;
    
    loop(i,0,n) {
        Int color = i + 1;
        S.push(i);
        visited[i] = true;
        if (colors[i] == 0) colors[i] = color;
        
out_of_while:
        while (!S.empty()) {
            Int i = S.top();
            for (auto c: vs[i]) {
                if (visited[c]) continue;
                S.push(c);
                visited[c] = true;
                if (colors[c] == 0) colors[c] = color;
                goto out_of_while;
            }
            
            S.pop();
        }
    }
}


int main(void) {
    Int n, m, q, v, x;
    cin >> n >> m;
    vector<Int> vs[n];
    Int colors[n];
    
    loop(i,0,m) {
        cin >> v >> x;
        vs[v].push_back(x);
        vs[x].push_back(v);
    } 
    
    dfs_color(vs, colors, n);
    
    cin >> q;
    loop(i,0,q) {
        cin >> v >> x;
        if (colors[v] == colors[x]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
}