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 <bits/stdc++.h>

using namespace std;

int main() {

	int n, m;
	cin >> n >> m;
	vector < vector<int>> G(n + 1);

	//グラフ隣接リスト読み込み
	int a, c;
	for (int i = 1; i <= m; i++) {
		cin >> a >> c;
		G[a].push_back(c);
		G[c].push_back(a);
	}

	//幅優先探索処理
	vector<bool> seen(n + 1, false);	//発見したらtrue
	deque<int> todo;					//行く所のスタック

	int s = 1;							//今いる場所

	bool brkflg;
	vector<long> color(n + 1);
	int colornum = 0;
	for (int j = 0; j < n; j++) {		//全ての頂点を調べる

		if (color[j] == 0) {
			colornum++;
			color[j] = colornum;
			brkflg = false;
			todo.clear();

			//for (int k = 0; k <= n; k++) {
			//	seen[k] = false;//一旦全クリア
			//}

			if (seen[j] == false) {			//訪れてなかったら処理すすめる
				seen[j] = true;
				todo.push_back(j);

				while (todo.empty() != true) {				//キューが空になるまで処理	
					s = todo.front();						//処理番号を指定
					int tugiflg = false;					//次があったらtrueにするフラグ
					for (int i = 0; i < G[s].size(); i++) {

						if (seen[G[s][i]] != true) {
							seen[G[s][i]] = true;
							color[G[s][i]] = colornum;
							todo.push_back(G[s][i]);
							tugiflg = true;
						}
					}
					todo.pop_front(); //次を全部探したので削除する
				}
			}
		}
	}

	int in1, in2;
	cin >> m;
	for (int i = 0; i <m; i++) {
		cin >> in1 >> in2;
		if (color[in1] == color[in2]) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

	return 0;

}

C++: #include <stdio.h>
#include <set>
#define MAX_USER (100000)

typedef std::set<long> Circle;

void merge_circle( Circle** circleinfo , long uid1 , long uid2 )
{
	Circle* src;
	Circle* dst;
	if( circleinfo[ uid1 ]->size() < circleinfo[ uid2 ]->size() )
	{
		src = circleinfo[ uid1 ];
		dst = circleinfo[ uid2 ];
	}
	else
	{
		src = circleinfo[ uid2 ];
		dst = circleinfo[ uid1 ];
	}

	Circle::const_iterator itr;
	for( itr = src->begin() ; itr != src->end() ; itr++ )
	{
		circleinfo[ *itr ] = dst;
		dst->insert( *itr );
	}
}

void add_member( Circle** circleinfo , long uid1 , long uid2 )
{
	if( circleinfo[ uid1 ] == 0 && circleinfo[ uid2 ] == 0 )
	{
		//create new circle
		Circle* entry = new Circle;
		entry->insert( uid1 );
		entry->insert( uid2 );

		circleinfo[ uid1 ] = entry;
		circleinfo[ uid2 ] = entry;
	}
	else if( circleinfo[ uid1 ] != 0 && circleinfo[ uid2 ] == 0 )
	{
		circleinfo[ uid1 ]->insert( uid2 );
		circleinfo[ uid2 ] = circleinfo[ uid1 ];
	}
	else if( circleinfo[ uid1 ] == 0 && circleinfo[ uid2 ] != 0 )
	{
		circleinfo[ uid2 ]->insert( uid1 );
		circleinfo[ uid1 ] = circleinfo[ uid2 ];
	}
	else
	{
		if( circleinfo[ uid1 ] != circleinfo[ uid2 ] )
		{
			merge_circle( circleinfo , uid1 , uid2 );
		}
	}
}

int main( int argc , char** argv )
{

	//read setting
	long user_count;
	long friendship_count;
	scanf( "%ld %ld" , &user_count , &friendship_count );

	//initialize
	Circle** user_info = new Circle*[ user_count ];
	for( long i = 0 ; i < user_count ; i++ )
	{
		user_info[ i ] = 0;
	}

	//read user friendship
	for( long i = 0 ; i < friendship_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		add_member( user_info , uid1 , uid2 );
	}

	//read number of question
	long question_count;
	scanf( "%ld" , &question_count );

	//process question
	for( long i = 0 ; i < question_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		if( user_info[ uid1 ] == user_info[ uid2 ] )
		{
			printf( "yes\n" );
		}
		else
		{
			printf( "no\n" );
		}
	}

	delete[] user_info;
	return 0;
}

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

bool DFS(const vector<vector<int> >& G, int a, int b) {
    stack<pair<int, int> > S;
    vector<bool> is_visited(G.size(), false);

    int idx = 0;
    do {
        if (G[a][idx] == b) return true;
        if (!is_visited[G[a][idx]]) {
            is_visited[G[a][idx]] = true;
            S.push(make_pair(a, idx));
            a   = G[a][idx];
            idx = 0;
            continue;
        }
        if (idx >= G[a].size()) {
            a   = S.top().first;
            idx = S.top().second;
            S.pop();
        }
        ++idx;
    } while (!S.empty());
    return false;
}


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

    vector<vector<int> > G(n);

    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }



    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        if (DFS(G, a, b)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}