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<vector>
#include<stack>
#include<queue>

struct node {
	int parent;
	std::vector<int> relation;
};

void dfs(std::vector<node> &n) {
	int d[100000];

	std::stack<int> s;
	for (size_t i = 0; i < n.size(); i++) {
		s.push(i);
		for (int k = 0; k < 100000; k++) {
			d[k] = 0;
		}
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			for (std::vector<int>::iterator it = n[num].relation.begin(); it != n[num].relation.end(); it++) {
				if (d[*it] == 1) {
					n[num].relation.erase(it);
					it--;
				} else {
					s.push(*it);
					d[*it] = 1;
				}
			}
		}
	}
}

void makeparent(std::vector<node> &n) {
	std::queue<int> q;
	for (size_t i = 0; i < n.size(); i++) {
		n[i].parent = -1;
	}
	for (size_t i = 0; i < n.size(); i++) {
		q.push(i);
		int parent = i;
		while (q.size() != 0) {
			parent = q.front(); q.pop();
			for (size_t j = 0; j < n[parent].relation.size(); j++) {
				q.push(n[parent].relation[j]);
				n[n[parent].relation[j]].parent = parent;
			}
		}
	}
}

bool isconnect(std::vector<node> n, int from, int to) {
	std::stack<int> s;
	while (n[from].parent != -1) {
		from = n[from].parent;
	}
	if (to == from) return true;
	s.push(from);
	while(s.size() != 0) {
		from = s.top(); s.pop();
		for (std::vector<int>::iterator it = n[from].relation.begin(); it != n[from].relation.end(); it++) {
			if (to == *it) return true;
			s.push(*it);
		}
	}
	return false;
}

int main() {
	int people, relation;
	
	std::cin >> people >> relation;

	std::vector<node> n(people);

	for (int i = 0; i < relation; i++) {
		int from, to;
		std::cin >> from >> to;
		n[from].relation.push_back(to);
		n[to].relation.push_back(from);
	}

	dfs(n);
	makeparent(n);

	/*
	for (size_t i = 0; i < n.size(); i++) {
		std::cout << i << " " << n[i].parent << std::endl;
	}

	for (size_t i = 0; i < n.size(); i++) {
		for (size_t j = 0; j < n[i].relation.size(); j++) {
			std::cout << i << n[i].relation[j] << std::endl;
		}
	}
	*/

	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		if (isconnect(n, from, to)) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
using namespace std;
#define N 100000

int group[N];
vector<int> vec[N];
int n,m;

int dfs_visit(int x,int k){
  stack<int> S;
  S.push(x);
  while(!S.empty()){
    int u=S.top();S.pop();
    for(int i=0;i<vec[u].size();i++){
      int v=vec[u][i];
      if(group[v]==0){
        group[v]=k;
        S.push(v);
      }
    }
  }
}
void dfs(){
  int id=1;
  for(int i=0;i<n;i++){
    if(group[i]==0) dfs_visit(i,id++);
  }
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
    int s,t;
    cin>>s>>t;
    vec[s].push_back(t);
    vec[t].push_back(s);
  }
  dfs();
  int q;
  cin>>q;
  for(int i=0;i<q;i++){
    int a,b;
    cin>>a>>b;
    if((group[a]!=0&&group[b]!=0)&&group[a]==group[b]){
      cout<<"yes"<<"\n";
    }else{
      cout<<"no"<<"\n";
    }
  }
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>
#include <set>
#include <list>
#include <cstring>
#include <stack>

using namespace std;

#define mod 1000000007

class UF
{
private:
	vector<int> root;

public:
	UF(int n)
	{
		root = vector<int>(n + 1, -1);
	}

	int getroot(int n)
	{
		if(root[n] == -1) return n;
		else return root[n] = getroot(root[n]);
	}

	void add(int x, int y)
	{
		x = getroot(x);
		y = getroot(y);
		if(x == y) return;
		if(x > y) swap(x, y);
		root[y] = x;
		return;
	}
};

int main()
{
	int n, m;
	cin >> n >> m;
	UF uf(n);
	for(int i = 0; i < m; i++){
		int s, t;
		cin >> s >> t;
		uf.add(s, t);
	}
	int q;
	cin >> q;
	for(int i = 0; i < q; i++){
		int s, t;
		cin >> s >> t;
		if(uf.getroot(s) == uf.getroot(t)) cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}