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 <stack>
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 r, int c)
{
	stack<int> S;
	S.push(r);
	color[r] = c;

	while (S.empty() == false) {
		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){
			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<vector>
#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include <iostream>
#include <algorithm>
#include <map>
#include <cmath>
#define INF 100000000000000
using namespace std;
typedef long long llong;

//int isalpha(char ch): ch がアルファベットなら true を返す
//int isdigit(char ch): ch が数字なら true を返す
//int islower(char ch): ch が小文字なら true を返す
//int isupper(char ch): ch が大文字なら true を返す
//int tolower(char ch): ch の小文字を返す
//int toupper(char ch): ch の大文字を返す

//string型
//size()	文字数を返す
//Insert()	（指定した場所に）文字・文字列を挿入する
//erase()	（指定した場所の）文字・文字列を削除する
//clear()	すべての文字を削除する
//substr()	文字列の（指定した）部分文字列を返す
//replace()	（指定した）部分文字列を新しい文字列に置換する
//文字列の比較は、<=や==などを使え
//replace関数を使い、簡単に文字列を置換
//リバース関数：reverse(str.begin(), str.end());
//map<type, type> dict;で宣言
//グラフ理論用変数
//vector<vector<llong> > graph(N);

//ソート
//降順sort(v.begin(), v.end(), std::greater<Type>());

//大文字から小文字へんかん
//w[i] = w[i]-'A'+'a';

//vector
//assignメソッド　引数：サイズ、値
//与えられたサイズと値でvectorを初期化する

void dfs(vector<vector<llong> > &graph, vector<bool> &seen, vector<llong> &color, llong node, llong now_color){
    if(seen[node]){
        return;
    }
    seen[node] = true;
    color[node] = now_color;
    for(int i=0; i<graph[node].size(); i++){
        dfs(graph, seen, color, graph[node][i], now_color);
    }
}

int main(){
    llong n,m;
    llong s,t;
    llong now_color=0;
    scanf("%lld %lld", &n, &m);
    vector<vector<llong> > graph(n);
    vector<bool> seen(n, false);
    vector<llong> color(n, 0);

    for(int i=0; i<m; i++){
        scanf("%lld %lld", &s, &t);
        graph[s].push_back(t);
        graph[t].push_back(s);
    }
    for(int i=0; i<n; i++){
        if(seen[i]){
            continue;
        }
        dfs(graph, seen, color, i, now_color);
        now_color++;
    }
    llong q;
    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 <stdio.h>

int m[100000] = {0};

void init() {
	int i;
	for ( i = 0; i < 100000; ++i) {
		m[i] = i;
	}
}

int find(int a) {
	if ( a == m[a]) {
		return a;
	}
	return m[a] = find(m[a]);
}

int friend(int x, int y) {
	if ( find(x) == find(y)) {
		return 1;
	} else {
		return 0;
	}
}

void unit (int x, int y) {
	x = find(x);
	y = find(y);
	
	if ( x == y ) {
		return ;
	}
	m[y] = x;
}

int main() {
	int n, s, t, u, v, i;
	init();
	scanf("%d", &n);
	scanf("%d", &s);
	
	for ( i = 0; i < s; i++) {
		scanf("%d %d", &u, &v);
		unit( u, v);
	}
	
	scanf("%d", &t);
	
	for ( i = 0; i < s; i++) {
		scanf("%d %d", &u, &v);
		if ( friend( u, v) == 1) {
			printf("yes\n");
		} else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<queue>
using namespace std;
#define MAX 100000
#define NIL -1

int n, m;
vector<int> V[MAX];
int color[MAX];

void search(int s){
  // init
  queue<int> Q;

  Q.push(s);
  int c = color[s] = s;
  while (!Q.empty()){
    int u = Q.front();
    Q.pop();
    for ( int i = 0; i < V[u].size(); i++){
      if ( color[V[u][i]] == NIL ){
        Q.push(V[u][i]);
        color[V[u][i]] = c;
      }
    }
  }
}

int main(){
  cin >> n >> m;

  int s, t;
  for (int i = 0; i < m; i++ ){
    cin >> s >> t;
    V[s].push_back(t);
    V[t].push_back(s);
  }

  for ( int i = 0; i < n; i++){ color[i] = NIL; }
  for ( int i = 0; i < n; i++){
    if ( color[i] == NIL){
      search(i);
    }
  }

  int q;
  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 <vector>
#include <cstdio>
class union_find{
	std::vector<int> parent;
public:
	int root(int a){return parent[a]==a?a:(parent[a]=root(parent[a]));}
	union_find(int n):parent(n+1){for(int i=1;i<=n;i++)parent[i]=i;}
	int same(int a,int b){return root(a)==root(b);}
	int unite(int a,int b){
		int x=root(a),y=root(b);//if(x==y)return 0;
		parent[x]=y;
		return 1;
	}
};
int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	union_find uf(n);
	int a,b;
	for(;m--;uf.unite(a,b))scanf("%d%d",&a,&b);
	for(scanf("%d",&m);m--;puts(uf.same(a,b)?"yes":"no"))scanf("%d%d",&a,&b);
}