Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

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

struct Node {
	int ID;
	int rep;
	bool visited;
	bool operator<(const Node& rhs) {return this->ID < rhs.ID;}
	bool operator>(const Node& rhs) {return this->ID > rhs.ID;}
	bool operator<=(const Node& rhs) {return this->ID <= rhs.ID;}
	bool operator>=(const Node& rhs) {return this->ID >= rhs.ID;}
	bool operator==(const Node& rhs) {return this->ID == rhs.ID;}
	bool operator!=(const Node& rhs) {return this->ID != rhs.ID;}
};

void BFS(std::vector<int>* adjlist, Node* nodes, std::queue<int> que)
{	
	while (!que.empty()) {
		int id = que.front(); que.pop();
		for (std::vector<int>::iterator it = adjlist[id].begin(); it != adjlist[id].end(); ++it) {
			if (!nodes[*it].visited) { 
				que.push(*it);
				nodes[*it].rep = nodes[id].rep;
				nodes[*it].visited = true;
			}
		}
	}
}

void DFS(std::vector<int>* adjlist, Node* nodes, int id, int rep)
{
	nodes[id].rep = rep;
	nodes[id].visited = true;
	
	for (std::vector<int>::iterator it = adjlist[id].begin(); it != adjlist[id].end(); ++it) {
		if (!nodes[*it].visited) DFS(adjlist, nodes, *it, rep);
	}
}

int main()
{
	int n, m; std::cin >> n >> m;
	
	std::vector<int>* adjlist = new std::vector<int>[n];
	Node* nodes = new Node[n];
	
	std::queue<int> que;
	
	for (int i=0; i<n; i++) {
		nodes[i].visited = false;
	}
	
	for (int i=0; i<m; i++) {
		int x, y;
		std::cin >> x >> y;
		adjlist[x].push_back(y);
		adjlist[y].push_back(x);
	}
	
	//std::sort(nodes, nodes + n);
	
	for (int i=0; i<n; i++) {
		if (!nodes[i].visited) {
			//que.push(i); nodes[i].visited = true; nodes[i].rep = i;
			//BFS(adjlist, nodes, que);
			DFS(adjlist, nodes, i, i);
		}
	}
	
	int q; std::cin >> q;
	
	for (int i=0; i<q; i++) {
		int x, y;
		std::cin >> x >> y;
		if (nodes[x].rep == nodes[y].rep) std::cout << "yes" << std::endl;
		else std::cout << "no" << std::endl;
	}
	
	delete[] adjlist;
	delete[] nodes;
	
	return 0;
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;


int n;

string *color = new string[n];

queue<int> q;

int *ans = new int[n];

vector<int> g[10000];





//int c[100][100];
/*
void bfs(int x){
  color[0] = "gray";
  d[0] = 0;

  q.push(0);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int v = 0; v < n; v++){
      if(c[u][v] == 1 && color[v] == "white"){
        color[v] = "gray";
        d[v] = d[u] + 1;
        q.push(v);
      }

    }

    color[u] = "black";
    ans[i++] = x;

  }
}
*/

void bfs(int x){
  color[x] = "gray";
  q.push(x);

  cout << "ok";


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int i = 0; i < g[u].size(); i++){
      int v = g[u][i];
      color[v] = "gray";
      q.push(v);
    }

    color[u] = "black";


  }
  for(int i = 0; i < n; i++){
    if(color[i] == "black"){
      ans[i] = x;
    }
  }
}


int main(){

  cin >> n;

  color = new string[n];

  int m;

  cin >> m;

  cout << n << m;


  int a, b;


  for(int i = 0; i < m; i++){

    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
    cout << i << "  " << m << endl;
  }

  cout << "ok";

  for(int i = 0; i < n; i++){
    color[i] = "white";
  }

  cout << "ok";


  for(int i = 0; i < n; i++){
    cout << "ok";
    if(color[i] == "white"){
      bfs(i);
    }
  }

  int q;

  /*cin >> q;

  for(int i = 0; i < q; i++){
    int a, b;
    cin >> a >> b;
    if(ans[a] == ans[b]){
      cout << "yes" << endl;
    }
    else{
      cout << "no" << endl;
    }
  }
*/





  return 0;
}

C++: #include <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <cmath>
#include <ctype.h>
#include <ctime>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <cctype>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <numeric>
#include <complex>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <iostream>
#include <iterator>
#include <algorithm>

using namespace std;
static const int MAX = 100000;
static const int INF = 1e9;

vector<int> V[MAX];
int n,m,s,t,q,d[MAX];

int bfs(int a,int b){
	for(int i = 0;i < n;i++) d[i] = INF;
	queue<int> qu;
	qu.push(a);
	d[a] = 0;
	while(!qu.empty()){
		int v = qu.front();qu.pop();
		for(int i = 0;i < n;i++){
			if(V[v][i] <= 0) continue;
			if(d[i] != INF) continue;
			d[i] = d[v] + 1;
			qu.push(i);
		}
	}
	return d[b];
}

int main(){
	cin >> n >> m;
	for(int i = 0;i < m;i++){
		cin >> s >> t;
		V[s].push_back(t);
		V[t].push_back(s);
	}
	cin >> m;
	for(int i = 0;i < m;i++){
		cin >> s >> t;
		if(bfs(s,t) != INF){
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}	
	return 0;
}

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

struct node {
	int parent;
	std::vector<int> relation;
};

void dfs(std::vector<node> &n) {
	int d[100000];

	std::stack<int> s;
	for (size_t i = 0; i < n.size(); i++) {
		s.push(i);
		for (int k = 0; k < 100000; k++) {
			d[k] = 0;
		}
		while (s.size() != 0) {
			int num = s.top(); s.pop();
			d[num] = 1;
			for (std::vector<int>::iterator it = n[num].relation.begin(); it != n[num].relation.end(); it++) {
				if (d[*it] == 1) {
					n[num].relation.erase(it);
					it--;
				} else {
					s.push(*it);
					d[*it] = 1;
				}
			}
		}
	}
}

void makeparent(std::vector<node> &n) {
	std::queue<int> q;
	for (size_t i = 0; i < n.size(); i++) {
		n[i].parent = -1;
	}
	for (size_t i = 0; i < n.size(); i++) {
		q.push(i);
		int parent = i;
		while (q.size() != 0) {
			parent = q.front(); q.pop();
			for (size_t j = 0; j < n[parent].relation.size(); j++) {
				q.push(n[parent].relation[j]);
				n[n[parent].relation[j]].parent = parent;
			}
		}
	}
}

bool isconnect(std::vector<node> n, int from, int to) {
	std::stack<int> s;
	while (n[from].parent != -1) {
		from = n[from].parent;
	}
	s.push(from);
	while(s.size() != 0) {
		from = s.top(); s.pop();
		for (std::vector<int>::iterator it = n[from].relation.begin(); it != n[from].relation.end(); it++) {
			if (to == *it) return true;
			s.push(*it);
		}
	}
	return false;
}

int main() {
	int people, relation;
	
	std::cin >> people >> relation;

	std::vector<node> n(people);

	for (int i = 0; i < relation; i++) {
		int from, to;
		std::cin >> from >> to;
		n[from].relation.push_back(to);
	}

	dfs(n);
	makeparent(n);

	/*
	for (size_t i = 0; i < n.size(); i++) {
		std::cout << i << " " << n[i].parent << std::endl;
	}
	*/
	int question;
	std::cin >> question;

	for (int i = 0; i < question; i++) {
		int from, to;
		std::cin >> from >> to;
		if (isconnect(n, from, to)) {
			std::cout << "yes" << std::endl;
		} else {
			std::cout << "no" << std::endl;
		}
	}

	return 0;
}