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++: //============================================================================
// Name        : Graph.cpp
// Author      : Ken
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

struct Node{
	int id;
	vector<int> adjNodes;
	bool isFound;
	int discover_time;
	int finish_time;
	int distance;
	int group_id;
};

class Graph{
public:
	vector<Node> nodeList;
	map<int, vector<Node*> > distanceMap;
	Graph():nodeList(), distanceMap(){}
	Graph(int n):nodeList(), distanceMap(){
		for(int i=0; i<n; i++){
			vector<int> empty_vec;
			Node node = {i, empty_vec, false, -1, -1, -1, -1};
			nodeList.push_back(node);
		}
	}

	void insert(Node& i){
		nodeList.push_back(i);
	}

	void SearchDepthFirst(int source_id, int& timer, int group_id){
		Node& source_node = nodeList.at(source_id);
		source_node.isFound = true;
		source_node.discover_time = timer;
		for(int i=0; i<source_node.adjNodes.size(); i++){
			if(nodeList.at(source_node.adjNodes.at(i)).isFound == false){
				timer ++;
				nodeList.at(source_node.adjNodes.at(i)).isFound = true;
				nodeList.at(source_node.adjNodes.at(i)).discover_time = timer;
				SearchDepthFirst(source_node.adjNodes.at(i), timer, group_id);
				nodeList.at(source_node.adjNodes.at(i)).finish_time = timer;
				nodeList.at(source_node.adjNodes.at(i)).group_id = group_id;
			}
		}
		timer++;

		source_node.finish_time = timer;
	}

	void SearchDepthFirstAll(int& timer){
		int group_id = 0;
		for(int i=0; i<nodeList.size(); i++){
			if(nodeList.at(i).isFound == false){
				nodeList.at(i).group_id = group_id;
				SearchDepthFirst(i, timer, group_id);
				timer++;
				group_id++;
			}
		}
	}

	void writeSearchResult(){
		for(int i=0; i<nodeList.size(); i++){
			cout << nodeList.at(i).id << " " << nodeList.at(i).group_id << "\n";
		}
	}


	void addDistance(){
		vector<Node*> vec;
		vec.push_back(&nodeList.at(0));
		distanceMap[0] =vec;
		int cur_distance=0;

		while(cur_distance < nodeList.size()){
			vector<Node*>& vec_p_node = distanceMap[cur_distance];
			vector<Node*> empty_vec;
			distanceMap[cur_distance+1] = empty_vec;
			for(int i=0; i<vec_p_node.size(); i++){
				vector<int>& adjNodes = vec_p_node.at(i)->adjNodes;
				for(int j=0; j<adjNodes.size(); j++){
					if(nodeList.at(adjNodes.at(j)).distance == -1){
					    nodeList.at(adjNodes.at(j)).distance = cur_distance+1;
					    distanceMap[cur_distance+1].push_back(&nodeList.at(adjNodes.at(j)));
					}
				}
			}
			if(distanceMap[cur_distance+1].size() == 0){
				break;
			}

			cur_distance++;
		}
	}

	void writeDistance(){
		for(int i=0; i<nodeList.size(); i++){
			cout << i+1 << " " << nodeList.at(i).distance << "\n";
		}
	}

	void write(){
		for(int i=0; i<nodeList.size(); i++){
			Node& node = nodeList.at(i);
			cout << node.id << " " << node.adjNodes.size() << " ";

			for(int j=0; j<node.adjNodes.size(); j++){
				cout << node.adjNodes.at(j) << " ";
			}
			cout << "\n";
		}

	}

	void writeMap(){
		map<int, vector<Node*> >::iterator p;
		for(p=distanceMap.begin(); p!=distanceMap.end(); ++p){
			cout << "distance: " << p->first << ", id: ";
			vector<Node*>::iterator p2;
			for(p2=p->second.begin(); p2!=p->second.end(); ++p2){
				cout << (*p2)->id << " ";
			}
			cout << "\n";
		}
	}
};

void writeMatrix(vector<vector<int> > matrix){
	for(int i=0; i<matrix.size(); i++){
		for(int j=0; j<matrix.at(i).size()-1; j++){
			cout << matrix.at(i).at(j) << " ";
		}
		cout << matrix.at(i).at(matrix.at(i).size()-1);
		cout << "\n";
	}
}

int main() {
	int n, m;
	cin >> n >> m;
	Graph g(n);

	for(int i=0; i<m; i++){
		int id_1, id_2;
		cin >> id_1 >> id_2;
		g.nodeList.at(id_1).adjNodes.push_back(id_2);
		g.nodeList.at(id_2).adjNodes.push_back(id_1);
	}

	//g.write();
	int timer = 1;
	g.SearchDepthFirstAll(timer);
	//g.writeSearchResult();

	int q;
	cin >> q;

	for(int i=0; i<q; i++){
		int qid_1, qid_2;
		cin >> qid_1 >> qid_2;
		if(g.nodeList.at(qid_1).group_id == g.nodeList.at(qid_2).group_id){
			cout << "yes\n";
		}else{
			cout << "no\n";
		}
	}

	//g.nodeList.at(0).distance = 0;
	//g.addDistance();
	//g.writeDistance();

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

bool dfs(int node, int gole, vector<vector<int> >& adjlist, vector<bool>& used){

    if(node == gole) return true;

    for(int i = 0; i < adjlist[node].size(); i++){
        if(used[adjlist[node][i]] == false){
            used[adjlist[node][i]] = true;
            return dfs(adjlist[node][i], gole, adjlist, used);
        }
    }

    return false;
}

int main(){

    int n, m; cin >> n >> m;

    vector<vector<int> > adjlist(n);               

    //入力
    for(int i = 0; i < m; i++){
        int a, b; cin >> a >> b;                   // a ←→ b に辺がある
        adjlist[a].push_back(b);
        adjlist[b].push_back(a);
        
    }

    //質問
    int q; cin >> q;
    for(int i = 0; i < q; i++){
        int a, b; cin >> a >> b;
        
        vector<bool> used(n, false);
        used[a] = true;
        if(dfs(a, b, adjlist, used)) cout << "yes" << endl;
        else cout << "no" << endl;
    }

    return 0;
}