Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

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

void boo(int b[], int y[], int w, int m){
	for(int i = 0; i < m; i++){
		if(b[i] == w) {
			if(y[b[i + m]] != -1){
				S.push(b[i + m]);
				y[b[i + m]] = 1;
			}
		}
	}
	for(int i = m; i < m * 2; i++){
		if(b[i] == w) {
			if(y[b[i - m]] != -1){
				S.push(b[i - m]);
				y[b[i - m]] = 1;
			}
		}
	}
}

int foo(int a, int s, int b[], int m, int n){
	int y[100100] = {}, i;

	
	S.push(a);
	y[a] = 1;
	
	while(S.empty() != true){
		i = S.top(); S.pop(); 
		if(i == s){
			return true;
		} else{
			y[i] = -1;
			boo(b, y, i, m);
		}
	}
	
	return false;
}

int main(){
	int b[200100];
	int n, m, q, a, s;
	int i, j, k;
	cin>>n>>m;
	for(i = 0; i < m; i++){
		cin>>b[i]>>b[m + i];
	}

	cin>>q;

	for(i = 0; i < q; i++){
		cin>>a>>s;
		if(foo(a, s, b, m, n) == 1){
			cout<<"yes"<<endl;
		} else {
			cout<<"no"<<endl;
		}
	}
	
	return 0;
}

C++: #include<iostream>    // ???????????????????§?????????£????????????
using namespace std;
#include<stdio.h>

typedef struct fox { int val; fox *prev, *next; } fox_t;

fox_t* init()
{
	fox_t* head = new fox_t;
	head->val = -1;
	head->next = NULL;
	head->prev = NULL;
	return head;
}

fox_t* make_tail(fox_t* head)
{
	fox_t* tail = new fox_t;
	tail->val = -1;
	head->next = tail;
	tail->next = NULL;
	tail->prev = head;
	return tail;
}

bool isEmpty(fox_t* head, fox_t* tail)
{
	return (head->next == tail ? true : false);
}

fox_t* b_insert(fox_t* tail, int data)
{
	fox_t* fox = new fox_t;
	fox->val = data;
	fox->prev = tail->prev;
	fox->next = tail;
	tail->prev->next = fox;
	tail->prev = fox;
	return fox;
}
// docking.
void unionfox(fox_t* head1, fox_t* tail1, fox_t* head2, fox_t* tail2)
{
	if(isEmpty(head1, tail1) || isEmpty(head2, tail2)) return;
	fox_t* fox = tail1->prev;
	cout << tail1->prev << endl;
	cout << head2->next << endl;
	fox->next = head2->next;
	head2->next->prev = fox;
	tail2->prev->next = tail1;
	tail1->prev = tail2->prev;
	delete tail2;
	delete head2;
}

int main()
{
	int color[101];
	int c_num = 0;
	fox_t* foxhead[101];
	fox_t* foxtail[101];
	int i, n, m, q;
	int a, b;
	cin >> n >> m;
	for(i = 0; i < n; i++){
		color[i] = -1;
		foxhead[i] = init();
		foxtail[i] = make_tail(foxhead[i]);
	}
	int c_a, c_b, val;

	for(i = 0; i < m; i++){
		cin >> a >> b;
		c_a = color[a];
		c_b = color[b];
		if(c_a < c_b) swap(a, b);  // color[a] >= color[b].
		if(c_a < 0 && c_b < 0){
			color[a] = c_num; color[b] = c_num;
			b_insert(foxtail[c_num], a);
			b_insert(foxtail[c_num], b);
			c_num++;
		}else if(c_b < 0){
			color[b] = c_a;
			b_insert(foxtail[c_a], b);
		}else if(c_a == c_b){
			continue;
		}else{ // color[a] != color[b].
			fox_t* fox = foxhead[c_b]->next;
			while(fox != foxtail[c_b]){
				val = fox->val;
				color[val] = c_a;
				fox = fox->next;
			};
			unionfox(foxhead[c_a], foxtail[c_a], foxhead[c_b], foxtail[c_b]);
		}
	}
	cin >> q;
	for(i = 0; i < q; i++){
		cin >> a >> b;
		if(color[a] >= 0 && (color[a] == color[b])){
			printf("yes\n"); }else{ printf("no\n"); 
			}
	}
	return 0;
}

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;

}