Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N, M := sc.nextInt(), sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < M; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	group := make([]int, N)
	for i := 0; i < N; i++ {
		group[i] = -1
	}
	var dfs func(cur int)
	dfs = func(cur int) {
		for i := 0; i < len(G[cur]); i++ {
			next := G[cur][i]
			if group[next] == -1 {
				group[next] = group[cur]
				dfs(next)
			}
		}
	}
	num := 0
	for i := 0; i < N; i++ {
		if group[i] == -1 {
			group[i] = num
			dfs(i)
			num++
		}
	}

	Q := sc.nextInt()
	for i := 0; i < Q; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		if group[s] == group[t] {
			fmt.Fprintln(wtr, "yes")
		} else {
			fmt.Fprintln(wtr, "no")
		}
	}
	wtr.Flush()
}

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

vector<int> list[100000];
int num[100000];
int n,m;

void bfs(int s,int sign){

  queue<int> Q;
  Q.push(s);

  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(num[temp]==-1){ //未訪問なら
        Q.push(temp); num[temp]=sign;
      }
    }
  }
}
int main(){

  cin>>n>>m;

  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  fill(num,num+100000,-1);
  int q; cin>>q;

  int sign=0;
  for(int i=0;i<n;i++){
    if(num[i]==-1){
      bfs(i,sign++);
    }
  }
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(num[s]==num[t] && (num[s]!=-1 || num[t]!=-1)){
      cout<<"yes\n";
    }else{
      cout<<"no\n";
    }
  }

}

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;
}