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 <stdio.h>
#include <iostream>
#include <list>
using namespace std;

class Node
{
private:
public:
	Node();
	int id;
	list<int> next_node_list;
	int next_idx;
	void AddNextNode(int id);
	void SetGroup(int prev_id, int num);
	int group;
	void Init(int id);
};

Node::Node()
{
	group = 0;
	next_idx = 0;
}

void Node::AddNextNode(int id)
{
	next_node_list.push_back(id);
}

Node *Node_list;

void Node::SetGroup(int prev_id, int num)
{
	group = num;

	list<int>::iterator itr;
	itr = next_node_list.begin();
	for (int i = 0; i < next_idx; i++) {
		itr++;
	}
	
	for(; itr != next_node_list.end(); itr++){
		next_idx++;
		if (prev_id != *itr) {
			Node_list[*itr].SetGroup(id, num);
		}
	}
}

void Node::Init(int id)
{
	this->id = id;
}

int main(void)
{
	//input
	int n;
	cin >> n;
	Node_list = new Node[n]();
	for (int i = 0; i < n; i++) {
		Node_list[i].Init(i);
	}
	int m;
	cin >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		Node_list[s].AddNextNode(t);
		Node_list[t].AddNextNode(s);
	}

	//group
	int group = 1;
	for (int i = 0; i < m; i++) {
		if (Node_list[i].group) continue;
		Node_list[i].SetGroup(-1, group);
		group++;
	}
	
	//output
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (Node_list[s].group == Node_list[t].group) {
			cout << "yes" << "\n";
		}
		else {
			cout << "no" << "\n";
		}
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)

int MAX = 100000;

vector<vector<int>> user(MAX, vector<int>(0));
vector<int> group(MAX, -1);

// 模範回答
// void dfs(int start, int group_i) {
//     stack<int> s;
//     group[start] = group_i;
//     s.push(start);
//     while (!s.empty()) {
//         int current = s.top();
//         s.pop();
//         for (int i = 0; i < user[current].size(); i++) {
//             int adj = user[current][i];
//             if (group[adj] == NIL) {
//                 s.push(adj);
//                 group[adj] = group_i;
//             }
//         }
//     }
// }

// 再帰によるdfs
void dfs(int start, int group_i) {
    group[start] = group_i;
    rep(i, user[start].size()) {
        int adj = user[start][i];
        if (group[adj] == -1) {
            dfs(adj, group_i);
        }
    }
}

// スタックによるdfsパターン1
// void dfs(int start, int group_i) {
//     stack<int> s;
//     group[start] = group_i;
//     s.push(start);
//     while (!s.empty()) {
//         int current = s.top();
//         group[current] = group_i;
//         bool stop = true;
//         for (int i = 0; i < user[current].size(); i++) {
//             int adj = user[current][i];
//             if (group[adj] == -1) {
//                 s.push(adj);
//                 stop = false;
//                 break;
//             }
//         }
//         if (stop) s.pop();
//     }
// }

int main() {
    int n, m, s, t, q;
    scanf("%d %d", &n, &m);
    rep(i, m) {
        scanf("%d %d", &s, &t);
        user[s].push_back(t);
        user[t].push_back(s);
    }

    int group_i = 0;
    rep(i, n) {
        if (group[i] == -1) {
            dfs(i, group_i++);
        }
    }

    scanf("%d", &q);
    rep(i, q) {
        scanf("%d %d", &s, &t);
        if (group[s] == group[t]) printf("yes\n");
        else printf("no\n");
    }
}

C++: #include <iostream>
#include <stack>
#include <vector>

using namespace std;

void dfs(vector<vector<int>>& g, vector<int>& color, int id, int c) {
    stack<int> s;
    vector<bool> visited(g.size(), false);
    s.push(id);
    color[id] = c;
    while (!s.empty()) {
        int id = s.top();
        s.pop();
        visited[id] = true;

        for (int i = 0; i < g[id].size(); ++i) {
            int adj = g[id][i];
            if (!visited[adj]) {
                color[adj] = c;
                s.push(adj);
            }
        }
    }
}

void assign_colors(vector<vector<int>>& g, vector<int>& color) {
    int color_id = 1;
    for (int i = 0; i < g.size(); ++i) {
        if (color[i] == -1) {
            dfs(g, color, i, color_id);
            ++color_id;
        }
    }
}

int main() {
    ios::sync_with_stdio(false);

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

    vector<vector<int>> g(n);
    for (int i = 0; i < m; ++i) {
        int p1, p2;
        cin >> p1 >> p2;
        g[p1].push_back(p2);
        g[p2].push_back(p1);
    }

    vector<int> color(n, -1);
    assign_colors(g, color);

    int p;
    cin >> p;
    for (int i = 0; i < p; ++i) {
        int p1, p2;
        cin >> p1 >> p2;
        if (color[p1] == color[p2])
            cout << "yes\n";
        else
            cout << "no\n";
    }
}

C++: #include <iostream>
#include <queue>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
using namespace std;

int n;

vector<int> uf;

void initialize(int n)
{
  uf = vector<int>(n);
  for (int i = 0; i < n; i++)
    uf[i] = i;
}

int root(int i)
{
  if (uf[i] == i) return i;
  return uf[i] = root(uf[i]);
}

void unite(int i, int j)
{
  int ri = root(i);
  int rj = root(j);
  if (ri != rj)
    uf[rj] = ri;
}

bool same(int i, int j)
{
  return root(i) == root(j);
}

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

  initialize(n);
  for (int i = 0; i < m; i++) {
    int u, v; cin >> u >> v;
    unite(u, v);
  }

  cin >> q;
  for (int i = 0; i < q; i++) {
    int u, v; cin >> u >> v;
    cout << (same(u, v)?"yes":"no") << endl;
  }

  return EXIT_SUCCESS;
}