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>
#include<algorithm>

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

void dfs(std::vector<node> &n) {
	std::stack<int> s;
	std::vector<int> d(n.size()), dd(n.size());
	for (size_t i = 0; i < n.size(); i++) {
		std::fill(d.begin(), d.end(), 0);
		s.push(i);
		if (dd[i] == 1)continue;
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			dd[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;
					std::vector<int>::iterator itt= std::find(n[*it].relation.begin(), n[*it].relation.end(), num);
					if (itt != n[*it].relation.end()) {
						n[*it].relation.erase(itt);
					}
				}
			}
		}
	}
}

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 (from == to) 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++: //
// Created by 李青坪 on 2018/11/4.
//

#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <string>

#define MAXN 100001
#define NIL -1
using namespace std;

vector<int > compo[MAXN];
int group[MAXN];
queue<int> queue1;

void init(int n){
    fill(group, group+n, NIL);
    queue1 = queue<int>();
}

void query(int node, int color){
    queue1.push(node);
    group[node] = color;
    int ex;
    while (!queue1.empty()){
        ex = queue1.front();
        queue1.pop();
        for (auto comp: compo[ex]){
            if (group[comp] != NIL) continue;
            group[comp] = color;
            queue1.push(comp);
        }
    }
}

void partitionGroup(int n){
    int c = 0;
    for (int i = 0; i < n; ++i) {
        queue1 = queue<int>();
        if (group[i] == NIL) query(i, c++);
    }
}

int main(){
    int n, m;
    scanf("%d %d", &n, &m);
    int s, t;
    for (int i = 0; i < m; ++i) {
        scanf("%d %d", &s, &t);
        compo[s].push_back(t);
        compo[t].push_back(s);
    }
    init(n);
    partitionGroup(n);
    int q;
    scanf("%d", &q);
    for (int j = 0; j < q; ++j) {
        scanf("%d %d", &s, &t);
//        printf("%d", group[s]);
        if (group[s] == group[t]) printf("yes\n");
        else printf("no\n");
    }
}
/*
10 5
0 1
1 2
2 9
3 4
6 7
12
0 1
0 2
0 9
3 4
6 7
7 6
0 5
0 6
3 7
3 5
5 8
8 5
 */

C++: #include <bits/stdc++.h>

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int id;
    int parent;
};

node person[100000];
vector<int> path;

int find(node x){
    if(x.parent == -1){
        REP(i, path.size())
            person[path[i]].parent = x.id;
        path.clear();
        return x.id;
    }
    else{
        path.push_back(x.id);
        return find(person[x.parent]);
    }
}

void marge(node x, node y){
    int x_id = find(x);
    int y_id = find(y);
    if(x_id == y_id)
        return;
    else
        person[y_id].parent = x_id;
    return;
}

bool judge(node x, node y){
    vector<int> xpath, ypath;
    return find(x) == find(y);
}

int main() {
    cin >> n >> m;
    REP(i, n){
        person[i].id = i;
        person[i].parent = -1;
    }
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[t].parent == -1)
            person[t].parent = person[s].id;
        else if(person[s].parent == -1)
            person[s].parent = person[t].id;
        else marge(person[s], person[t]);
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(judge(person[s], person[t]))
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}