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 <cstdint>
#include <vector>

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[i].connections.size(); i++) {
      colorize(graph[i].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection()
{
  for (uint32_t i = 0; i < GRAPH_SIZE; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 0;
  for (uint32_t i = 0; GRAPH_SIZE; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
  }

  check_connection();

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include<stdio.h>
using namespace std;

const int MAX = 100001;

int parent(int table[], int child) {
	if (table[child] == 0)return child;
	return table[child] = parent(table, table[child]);
}

int main() {
	int n, m, q;
	int table[MAX] ={0};

	scanf("%d %d", &n, &m);

	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &s, &t);
		s++;t++;
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		int s, t;
		
		scanf("%d %d", &s, &t);
                s++;t++;
		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_set>

using namespace std;

template<typename ISTREAM>
void readGraphListFromFriendInfo(ISTREAM& cin, vector< vector<int> >& friendGraphList) {
	size_t n;
	cin >> n;
	friendGraphList = vector< vector<int> >(n);
	size_t m;
	cin >> m;
	for (size_t i = 0; i != m; ++i) {
		size_t s,t;
		cin >> s >> t;
		friendGraphList.at(s).push_back(t);
		friendGraphList.at(t).push_back(s);
	}
	for (auto& v : friendGraphList)v.shrink_to_fit();
}

void accesibleNodeSearch(const vector<vector<int>>& graphList, vector<vector<int>>& visitMatrix, const int s) {
	const size_t n = graphList.size();
	queue<int> nodeQueue;
	vector<bool> visitList;
	visitList.resize(n, false);
	nodeQueue.push(s);
	visitList.at(s).flip();
	while (!nodeQueue.empty()) {
		const int id = nodeQueue.front();
		const vector<int>& adjList = graphList.at(id);
		for (const auto& adjID : adjList) {
			if (visitList.at(adjID))continue;
			const vector<int>& idList = graphList.at(adjID);
			if (find(idList.begin(), idList.end(), id) == idList.end())continue;
			nodeQueue.push(adjID);
			visitList.at(adjID).flip();
		}
		nodeQueue.pop();
	}
	const int num = count(visitList.begin(), visitList.end(), true);
	visitMatrix.at(s).reserve(num);
	for (int i = 0; i != n; ++i) {
		if (!visitList.at(i))continue;
		visitMatrix.at(s).push_back(i);
	}
}

void buildFriendAccesibility(const vector<vector<int>>& graphList, vector<vector<int>>& visitMatrix) {
	const int n = graphList.size();
	visitMatrix.resize(n, vector<int>());
	for (int i = 0; i != n; ++i) {
		accesibleNodeSearch(graphList, visitMatrix, i);
	}
}

template<typename T>
void execute(T& cin) {
	vector< vector<int> > graphList;
	readGraphListFromFriendInfo(cin, graphList);
	vector<vector<int>> visitMatrix;
	buildFriendAccesibility(graphList, visitMatrix);
	int q, s, t;
	cin >> q;
	for (int i = 0; i != q; ++i) {
		cin >> s >> t;
		cout << ( find(visitMatrix.at(s).begin(), visitMatrix.at(s).end(),t) != visitMatrix.at(s).end() ? "yes" : "no") << endl;
	}
}

int main()
{


	execute(cin);

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int N;
vector<int> par;
void init(int m)
{
    N = m;
    par.resize(N);
    for (int i = 0; i < N; ++i) par[i] = i;
}
int find(int x) {
    return (par[x] == x) ? x : (par[x] = find(par[x]));
}
int isunion(int x, int y) {
    return find(x) == find(y);
}
int tounion(int x, int y)
{
    int p = find(x), q = find(y);
    if (p == q) return 0;
    par[q] = p;
    return 1;
}

int main() {
    int n, m, q;
    cin >> n >> m;
    init(n);
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        tounion(a, b);
    }
    cin >> q;
    for (int i = 0; i < q; ++i) {
        int a, b;
        cin >> a >> b;
        cout << (isunion(a, b) ? "yes\n" : "no\n");
    }
    return 0;
}