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 <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

#define rep(i,n)   for (int i = 0; i < (n); ++i)
#define sort(a)    sort((a).begin(), (a).end());
#define uniq(a)    SORT(a);(a).erase(unique((a).begin(), (a).end()), (a).end());
#define find(a,x)  find((a).begin(), (a).end(), (x)) != (a).end()
#define reverse(a) reverse((a).begin(), (a).end());
#define out(d) cout << (d);
#define outl(d) std::cout<<(d)<<"\n";
#define Yes() printf("Yes\n");
#define No() printf("No\n");
#define YES() printf("YES\n");
#define NO() printf("NO\n");
#define ceil(x, y) ((x + y - 1) / (y))

using namespace std;
using ll = long long;
using P = pair<ll,ll>;

static const ll MOD = 1000000007; // 10^9 + 7
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;
  rep(i, n) color[i] = NIL;
  rep(u, n) {
    if (color[u] == NIL) dfs(u, id++);
  }
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  srand((unsigned)time(NULL));

  int s, t, m, q;
  cin >> n >> m;

  rep(i, m) {
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

  cin >> q;

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

C++: #include<cstdio>
#include<vector>
using namespace std;
#define MAX 100000;

void DepthFirstSearch(int present_vertex, bool has_not_been_discovered[], vector<int> Adjacency_list[], int Group_number[], int group_number){
	int pv = present_vertex;
	has_not_been_discovered[pv] = false;
	Group_number[pv] = group_number;
	for(int i = 0;i < Adjacency_list[pv].size();++i){
		if(has_not_been_discovered[Adjacency_list[pv][i]]){
			DepthFirstSearch(Adjacency_list[pv][i], has_not_been_discovered, Adjacency_list, Group_number, group_number);
		}
	}
}

void DfsInit(int n, bool has_not_been_discovered[]){
	for (int i = 0; i < n; ++i)
		has_not_been_discovered[i] = true;
}

int main(){
	int number_of_users, number_of_friendships;
	scanf("%d %d", &number_of_users, &number_of_friendships);
	vector<int> Adjacency_list[number_of_users];
	for (int i = 0; i < number_of_friendships; ++i)	{
		int friend1, friend2;
		scanf("%d %d", &friend1, &friend2);
		Adjacency_list[friend1].push_back(friend2);
		Adjacency_list[friend2].push_back(friend1);
	}
	bool has_not_been_discovered[number_of_users];
	DfsInit(number_of_users, has_not_been_discovered);
	int Group_number[number_of_users];
	int group_number = 1;
	for (int user_i = 0; user_i < number_of_users; ++user_i){
		if(has_not_been_discovered[user_i])
			DepthFirstSearch(user_i, has_not_been_discovered, Adjacency_list, Group_number, group_number++);
	}
	int number_of_questions;
	scanf("%d", &number_of_questions);
	for (int i = 0; i < number_of_questions; ++i) {
		int user1, user2;
		scanf("%d %d", &user1, &user2);
		if(Group_number[user1] == Group_number[user2])
			printf("yes\n");
		else
			printf("no\n");
	}
	return 0;
}