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>
using namespace std;
static const int N = 100000;
static const int NIL = -1;
int n;
vector<int> G[N];
int reach[N];
void dfs(int r, int c) {
    stack<int> S;
    S.push(r);
    reach[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 (reach[v] == NIL) {
                reach[v] = c;
                S.push(v);
            }
        }
    }
}
void assign() {
    int id = 1;
    for (int i = 0; i < n; i++) reach[i] = NIL;
    for (int u = 0; u < n; u++)
        if (reach[u] == NIL) dfs(u, id++);
}
int main() {
    int s, t, m, q;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    assign();
    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> s >> t;
        if (reach[s] == reach[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

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

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)
				y[b[i + m]] = 1;
		}
	}
	for(int i = m; i < m * 2; i++){
		if(b[i] == w) {
			if(y[b[i - m]] != -1)
				y[b[i - m]] = 1;
		}
	}
}

int foo(int a, int s, int b[], int m, int n){
	int z = 0, y[100100] = {}, k = 1;
	y[a] = 1;
	while(k){
		k = 0;
		for(int i = 0; i < n; i++){
			if(y[i] == -1) continue;
			else if(y[i] == 1){ 
				if(i == s){
					z = 1;
					k = 0;
					break;
				} else{
					k = 1;
					y[i] = -1;
					boo(b, y, i, m);
				}
			}
		}
	}
	return z;
	
}

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 <bits/stdc++.h>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int> G[MAX];
int color[MAX];

void dfs(int topId, int c) {
    stack<int> S;
    S.push(topId);
    color[topId] = 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;
    for (int i = 0; i < n; i++) color[i] = NIL;
    for (int u = 0; u < n; u++) {
        if (color[u] == NIL) dfs(u, id++);
    }
}

int main() {
    int s, t, m, q;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    assignColor();

    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> s >> t;
        if (color[s] == color[t]) {
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }

    return 0;
}

C++: #include <stack>
#include <stdio.h>
#include <vector>

using namespace std;

#define NMAX 100000
#define NIL -1

int n;
stack<int> S;
vector<int> adj[NMAX + 1]; // 0-origin
int d[NMAX + 1];           // if visited
int c[NMAX + 1];           // color

int next_unvisited() {
    for (int i = 0; i < n; i++) {
        if (d[i] == 0)
            return i;
    }
    return NIL;
}

int next_unvisited_adj(int u) {
    vector<int>::iterator it;
    for (it = adj[u].begin(); it != adj[u].end(); it++) {
        if (d[*it] == 0)
            return *it;
    }
    return NIL;
}

void dfs() {
    int x; // start vertex;
    int round = 0;
    while ((x = next_unvisited()) != NIL) {
        d[x] = 1;
        c[x] = round;
        S.push(x);
        while (!S.empty()) {
            int u = S.top();
            int v = next_unvisited_adj(u);
            if (v != NIL) {
                if (d[v] == 0) {
                    d[v] = 1;
                    c[v] = round;
                    S.push(v);
                }
            } else {
                S.pop();
            }
        }
        round++;
    }
}

int main() {
    int m, q, u, v;
    scanf("%d %d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d %d", &u, &v);
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int i = 0; i < n; i++)
        d[i] = 0;
    dfs();
    scanf("%d", &q);
    for (int i = 0; i < q; i++) {
        scanf("%d %d", &u, &v);
        if (c[u] == c[v])
            printf("yes\n");
        else
            printf("no\n");
    }
    return 0;
}