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 <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_map>

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();
}

const vector<int>& accesibleNodeSearch(const vector<vector<int>>& graphList
	, unordered_map<int, vector<int>>& visitMatrix
	, const int s
	, vector<bool>& visitList) 
{
	pair<unordered_map<int, vector<int>>::iterator, bool> result = visitMatrix.emplace(s,vector<int>());
	vector<int>& visitIDList = result.first->second;
	if (result.second) {//未計算の場合のみ計算する
		const size_t n = graphList.size();
		queue<int> nodeQueue;
		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);
		visitIDList.reserve(num);
		for (int i = 0; i != n; ++i) {
			if (!visitList.at(i))continue;
			visitIDList.push_back(i);
		}
	}
	return visitIDList;
}

template<typename T>
void execute(T& cin) {
	vector< vector<int> > graphList;
	readGraphListFromFriendInfo(cin, graphList);
	unordered_map<int, vector<int>> visitMatrix;
	vector<bool> visitList;
	int q, s, t;
	cin >> q;
	for (int i = 0; i != q; ++i) {
		cin >> s >> t;
		const vector<int>& idList = accesibleNodeSearch(graphList, visitMatrix, s, visitList);
		cout << ( find(idList.cbegin(), idList.cend(),t) != idList.cend() ? "yes" : "no") << endl;
	}
}

int main()
{


	execute(cin);



	return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <vector>
#include <stack>
using namespace std;
const int num = 100001;
vector<int> v[num];
int n;
int co[num];
inline void dfs(int t, int c) {
	stack<int> st;
	st.push(t);
	co[t] = c;
	while (!st.empty()) {
		int u = st.top(); st.pop();
		for (int i = 0; i < v[u].size(); i++) {
			int g = v[u][i];
			cout << g << endl;
			if (co[g] == 0) {
				co[g] = c;
				st.push(g);
			}
		}
	}
}
int main() {
	int m, s, t, q, id = 0, a, b;
	cin >> n >> m;
	for (int i = 0; i < n; i++)
		co[i] = 0;
	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++) {
		if (co[i] == 0) {
			id++;
			dfs(i, id);
		}
	}
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> a >> b;
		if (co[a] == co[b])
			cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<deque>
#define NOT_VISITED -1
using namespace std;

int main(){
  vector<vector<int> > path;
  vector<int> visited;
  int n,m,q;

  cin >> n >> m;
  path.resize(n);
  visited.resize(n);
  for(int j=0;j<n;j++){
    visited[j]=NOT_VISITED;
  }
  for(int i=0;i<m;i++){
    int s,t;

    cin >> s >> t;
    path[s].push_back(t);
    path[t].push_back(s);
  }

  cin >> q;
  for(int i=0;i<q;i++){
    deque<int> que;
    int s,t;
    
    cin >> s >> t;
    if(visited[s]==NOT_VISITED){
      visited[s]=s;
      que.push_back(s);
      while(!que.empty()){
        int myplace=que.front();

        que.pop_front();
        for(int j=0;j<path[myplace].size();j++){
          int to=path[myplace][j];
	
	  if(visited[to]==NOT_VISITED){
            visited[to]=s;
	    que.push_back(to);
	  }
        }
      }
    }

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

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

typedef struct box { int val; box *prev, *next; } box_t;

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

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

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

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[100][100];
    int dist[100];

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes"); }else{ printf("no"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

    return 0;
}