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>    // ???????????????????§?????????£????????????
using namespace std;
#include<stdio.h>

typedef struct fox { int val; fox *prev, *next; } fox_t;

fox_t* init()
{
	fox_t* head = new fox_t;
	head->val = -1;
	head->next = NULL;
	head->prev = NULL;
	return head;
}

fox_t* make_tail(fox_t* head)
{
	fox_t* tail = new fox_t;
	tail->val = -1;
	head->next = tail;
	tail->next = NULL;
	tail->prev = head;
	return tail;
}

bool isEmpty(fox_t* head, fox_t* tail)
{
	return (head->next == tail ? true : false);
}

fox_t* b_insert(fox_t* tail, int data)
{
	fox_t* fox = new fox_t;
	fox->val = data;
	fox->prev = tail->prev;
	fox->next = tail;
	tail->prev->next = fox;
	tail->prev = fox;
	return fox;
}
// docking.
void unionfox(fox_t* head1, fox_t* tail1, fox_t* head2, fox_t* tail2)
{
	if(isEmpty(head1, tail1) || isEmpty(head2, tail2)) return;
	fox_t* fox = tail1->prev;
	cout << tail1->prev << endl;
	cout << head2->next << endl;
	fox->next = head2->next;
	head2->next->prev = fox;
	tail2->prev->next = tail1;
	tail1->prev = tail2->prev;
	delete tail2;
	delete head2;
}

int main()
{
	int color[101];
	int c_num = 0;
	fox_t* foxhead[101];
	fox_t* foxtail[101];
	int i, n, m, q;
	int a, b;
	cin >> n >> m;
	for(i = 0; i < n; i++){
		color[i] = -1;
		foxhead[i] = init();
		foxtail[i] = make_tail(foxhead[i]);
	}
	int c_a, c_b, val;

	for(i = 0; i < m; i++){
		cin >> a >> b;
		c_a = color[a];
		c_b = color[b];
		if(c_a < c_b) swap(a, b);  // color[a] >= color[b].
		if(c_a < 0 && c_b < 0){
			color[a] = c_num; color[b] = c_num;
			b_insert(foxtail[c_num], a);
			b_insert(foxtail[c_num], b);
			c_num++;
		}else if(c_b < 0){
			color[b] = c_a;
			b_insert(foxtail[c_a], b);
		}else if(c_a == c_b){
			continue;
		}else{ // color[a] != color[b].
			fox_t* fox = foxhead[c_b]->next;
			while(fox != foxtail[c_b]){
				val = fox->val;
				color[val] = c_a;
				fox = fox->next;
			};
			unionfox(foxhead[c_a], foxtail[c_a], foxhead[c_b], foxtail[c_b]);
		}
	}
	cin >> q;
	for(i = 0; i < q; i++){
		cin >> a >> b;
		if(color[a] >= 0 && (color[a] == color[b])){
			printf("yes\n"); }else{ printf("no\n"); 
			}
	}
	return 0;
}

C++: #include <stdio.h>
#include <stdint.h>
#include <iostream>
#include <fstream>
#include <cassert>
#include <climits>

#include <cstring>
#include <queue>
using namespace std;

#define DEBUG (0)

#if DEBUG
#define DPRINTF(...) do { \
    printf("D(L%d) %s: ", __LINE__, __func__); \
    printf(__VA_ARGS__); \
  } while (false)
#else
#define DPRINTF(...)
#endif // DEBUG


const int kInvalid = -1;
const int kMaxUsers = 100 * 1000 + 1;

int g_group[kMaxUsers]; // 400 KiB

// 100 K * sizeof(vector<int>) + 100 K * sizeof(int)
// = 2.4 MiB + 100 K * sizeof(int)
vector<int> g_list[kMaxUsers];

void setRelations(int start, int end)
{
  g_list[start].push_back(end);
  g_list[end].push_back(start);
}


void doGrouptize()
{
  // debug info
  DPRINTF("size of g_group[] %lu Byte\n", sizeof(g_group));
  DPRINTF("size of g_list[]  %lu Byte\n", sizeof(g_list));

  // init
  int groupId = 0;
  //memset(g_group, kInvalid, kMaxUsers);
  for (int i = 0; i < kMaxUsers; i++)
    g_group[i] = kInvalid;

  for (int i = 0; i < kMaxUsers; i++)
  {
    if (g_group[i] != kInvalid)
      continue;

    g_group[i] = groupId;

    // grouptize connected users in BFS order
    queue<int> que;
    que.push(i);

    while (!que.empty())
    {
      const int current = que.front();
      que.pop();

      for (int j = 0; j < g_list[current].size(); j++)
      {
        const int next = g_list[current][j];

        if (g_group[next] != kInvalid)
          continue;

        g_group[next] = groupId;
        que.push(next);
      }
    }

    groupId++;
  }
}


void printAllRelations()
{
#if DEBUG
  for (int i = 0; i < kMaxUsers; i++)
  {
    for (int j = 0; j < g_list[i].size(); j++)
    {
      if (j == 0)
        DPRINTF("%d", i);

      printf(" %d", g_list[i][j]);

      if (j == g_list[i].size() - 1)
        cout << endl;
    }
  }
#endif // DEBUG
}


int main()
{
  int n, m;
  cin >> n >> m; cin.ignore();

  DPRINTF("number of users %d\n", n);
  DPRINTF("number of relations %d\n", m);

  for (int i = 0; i < m; i++)
  {
    int s, t;
    cin >> s >> t; cin.ignore();

    setRelations(s, t);
  }

  printAllRelations();

  doGrouptize();

  int q;
  cin >> q; cin.ignore();

  for (int i = 0; i < q; i++)
  {
    int s, t;
    cin >> s >> t; cin.ignore();

    DPRINTF("src %d  dst %d\n", s, t);

    if (g_group[s] == g_group[t])
      cout << "yes" << endl;
    else
      cout << "no" << endl;
  }

  return 0;

}

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


std::vector<int> V[100000];
int C[100000];
int color;
int maxi;

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

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

    for (int i = 0; i < n; i++) {
        if(C[i] == 0) {
            color++;
            std::queue<int> Q;
            Q.push(i);
            while (Q.size()) {
                C[Q.front()] = color;
                for (auto t: V[Q.front()]) {
                    if (C[t] == 0) {
                        C[t] = color;
                        Q.push(t);
                    }
                }
                Q.pop();
            }
        }
    }

    std::cin >> q;
    for (int i = 0; i < q; i++) {
        int s, t;
        std::cin >> s >> t;
        if ((C[s] == C[t]) && (C[s] != 0)) {
            std::cout << "yes" << std::endl;
        }
        else{
            std::cout << "no" << std::endl;
        }
    }

}

C++: #include <iostream>
#include<stack>
#include<queue>
using namespace std;
const int MAXn=100000;
const int NIL=-1;

int n,col[MAXn];
vector<int> G[MAXn];

void dfs(int r,int c)
{
	stack<int> S;
	S.push(r);
	col[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(col[v]==NIL)
			{
				col[v]=c;
				S.push(v);
			}
		}
	}
	return;
}

void assigncol()
{
	int id=1;
	for(int i=0;i<n;i++)col[i]=NIL;
	for(int u=0;u<n;u++)if(col[u]==NIL)dfs(u,id++);
	return;
}

int main() {
	int m,a,b,q;cin>>n>>m;
	for(int i=0;i<m;i++)
	{
		cin>>a>>b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	assigncol();
	cin>>q;
	for(int i=0;i<q;i++)
	{
		cin>>a>>b;
		if(col[a]==col[b])cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}