Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

func (q *Queue) isEmpty() bool {
	return q.head == nil
}

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: #include <iostream>
#include <vector>
#define eol '\n'
using namespace std;

vector<int> group;

void bfs(int v, int g, vector< vector<int> > list) {
  if (group[v] != 0) {
    return;
  }
  group[v] = g;
  for (int i = 0; i < list[v].size(); i++) {
    bfs(list[v][i], g, list);
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);

  int n,m,s,t,q;
  cin >> n >> m;

  vector< vector<int> > list(n, vector<int>());
  group = vector<int>(n,0);
  
  for (int i = 0; i < m; i++) {
    cin >> s >> t;
    list[s].push_back(t);
    list[t].push_back(s);
  }

  int g = 1;
  for (int i = 0; i < n; i++) {
    if (group[i] == 0) {
      bfs(i, g, list);
      g++;
    }
  }

  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> s >> t;
    if (group[s] == group[t]) {
      cout << "yes" << eol;
    } else {
      cout << "no" << eol;
    }
  }
  return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vl = vector<ll>;
using vll = vector<vector<ll>>;
using pii = pair<int,int>;
#define FOR(i,a,b) for(ll i = (a); i < (b); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(obj) (obj).begin(), (obj).end()
#define pb push_back
const double PI = acos(-1);
const double EPS = 1e-10;
const ll MOD = 1000000007;
void cioacc(){//accelerate cin/cout
  cin.tie(0);
  ios::sync_with_stdio(false);
}
struct union_find{//rank,経路圧縮で高速化
  vi par;//parは添字の親（または自分が根の時自身）を示す。
  vi rank;//rankは木の高さ（根についてのみ実装）
  union_find(int n){
    par.assign(n,0);
    rank.assign(n,0);
    REP(i,n) par[i]=i;
  }
  int find(int a){//根を探す
    if(par[a]==a) return a;
    else return par[a] = find(par[a]);//根に直接つける
  }
  void unite(int a,int b){//小さい方の木の根に大きい方の根を上書きする
    int roota,rootb;
    roota = find(a),rootb = find(b);
    if(roota==rootb) return;
    if(rank[roota]>rank[rootb]){
      par[rootb] = roota;
    }else if(rank[roota]<rank[rootb]){
      par[roota] = rootb;
    }else{
      rank[roota]++;
      par[rootb] = roota;
    }
  }
};
int main(){
  cioacc();
  int n,m;
  cin >> n >> m;
  union_find uf(n);
  REP(i,m){
    int tmp1, tmp2;
    cin >> tmp1 >> tmp2;
    uf.unite(tmp1,tmp2);
  }
  int q;
  cin >> q;
  REP(i,q){
    int tmp1,tmp2;
    cin >> tmp1 >> tmp2;
    if(uf.find(tmp1)==uf.find(tmp2)) cout << "yes" << endl;
    else cout << "no" << endl;
  }
}

C++: #include<iostream>
#include<cstring>
using namespace std;

bool x[10000][10000];
bool y[10000];

int main(){
	int n,m,a,b,q;
	cin>>n>>m;
	for(int i=0;i<m;i++){
		cin>>a>>b;
		x[a][b]=true;
		x[b][a]=true;
	}
	cin>>q;
	for(int h=0;h<q;h++){
		cin>>a>>b;
		memset(y,0,sizeof(y));
		y[a]=true;
		for(int i=0;i<50;i++){
			for(int j=0;j<n;j++){
				if(y[j]==true){
					for(int k=0;k<n;k++){
						if(x[j][k]==true){
							y[k]=true;
						}
					}
				}
				if(y[b]==true){
					cout<<"yes"<<endl;
					goto Exit;
				}
			}
		}
		cout<<"no"<<endl;
		Exit:;
	}
	return 0;
}

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

class TUser
{
	std::vector<TUser*> FAccessible;
public:
	void AddFriend(TUser* Friend);
	bool IsAccesible(const TUser* Target)const;
};

void TUser::AddFriend(TUser* Friend)
{
	if(IsAccesible(Friend)) return;
	FAccessible.push_back(Friend);
	for(unsigned int i = 0; i < FAccessible.size(); ++i){
		FAccessible[i]->AddFriend(Friend);
	}
}

bool TUser::IsAccesible(const TUser* Target)const
{
	return std::find(FAccessible.begin(), FAccessible.end(), Target) != FAccessible.end();
}

class TSns
{
	std::vector<TUser> FUsers;
public:
	TSns(int UserCount);
	
	void AddLink(int UserA, int UserB);
	std::string IsAccesible(int UserA, int UserB)const;
};

TSns::TSns(int UserCount)
: FUsers(UserCount)
{
}

void TSns::AddLink(int UserA, int UserB)
{
	FUsers[UserA].AddFriend(&FUsers[UserB]);
	FUsers[UserB].AddFriend(&FUsers[UserA]);
}

std::string TSns::IsAccesible(int UserA, int UserB)const
{
	if(FUsers[UserA].IsAccesible(&FUsers[UserB])) return "yes";
	return "no";
}

int main()
{
	int UserCount;
	std::cin >> UserCount;
	TSns Sns(UserCount);
	
	int LinkCount;
	std::cin >> LinkCount;
	for(int i = 0; i < LinkCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		Sns.AddLink(UserA, UserB);
	}
	
	int QuestionCount;
	std::cin >> QuestionCount;
	for(int i = 0; i < QuestionCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		std::cout << Sns.IsAccesible(UserA, UserB) << std::endl;
	}
	return 0;
}