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 <cstdio>
#include <algorithm>
#include <unordered_set>
#include <vector>

int main(){
    int n;
    int m;
    std::scanf("%d", &n);
    std::scanf("%d", &m);
    std::vector<std::unordered_set<int> > relations;
    for(int i = 0; i < m; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        int finds = -1;
        int findt = -1;
        for(int j = 0; j < relations.size(); ++j){
            if(relations[j].find(s) != relations[j].end()){
                finds = j;
            }
            if(relations[j].find(t) != relations[j].end()){
                findt = j;
            }
            if(findt != -1 && finds != -1) break;
        }
        for(int j = 0; j < relations.size(); ++j){
        }
        if(finds == -1 && findt == -1){
            std::unordered_set<int> set;
            set.insert(s);
            set.insert(t);
            relations.push_back(set);
        } else if(findt == -1){
            relations[finds].insert(t);
        } else if(finds == -1){
            relations[findt].insert(s);
        } else if(finds != findt){

            int smaller = (relations[finds].size() < relations[findt].size()) ? finds : findt;
            int larger = (smaller == findt) ? finds : findt;
            for(auto &x: relations[smaller]){
                relations[larger].insert(x);
            }
            relations[smaller] = relations.back();
            relations.pop_back();
        }
    }
    int q;
    std::scanf("%d", &q);
    for(int i = 0; i < q; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        bool find = false;
        for(int j = 0; j < relations.size(); ++j){
            if(relations[j].find(s) != relations[j].end() && relations[j].find(t) != relations[j].end()){
                find = true;
		break;
            }
        }
        if(find){
            std::printf("yes\n");
        } else {
            std::printf("no\n");
        }
    }

    return 0;
}

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

int n;
vector<int> G[MAX];
int color[MAX];

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

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


int main()
{
	int s, t, m, q;
	cin >> n >> m;
	
	for(int i = 0; i < m; i++)
	{
		cin >> s >> t;
		G[s].push_back(t);
		G[t].push_back(s);
	}
	
	assignColor();
	
	cin >> q;
	for(int i = 0; i < q; i++)
	{
		cin >> s >> t;
		if(color[s] == color[t])
		{
			cout << "yes" << endl;
			
		}
		else
		 cout << "no" << endl;
	}
}

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

int main(){
  int n,m,q,a,b,s,t,k,h;
  vector<int> g[100001];
  queue<int> qu;
  set<int> ch;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>a>>b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    
    k=0; 
    ch.clear();
    while(qu.size()){
      qu.pop();
    }
    qu.push(s);
    
    while(qu.size()){//?????????
      n=qu.front();qu.pop();
      if(n==t){//???????????????
	cout<<"yes"<<endl;
	k++;
	break;
      }
      for(int j=0;j<g[n].size();j++){//????????????????????´????????????
	if(ch.count(g[n][j])==0 ){
	  qu.push(g[n][j]);
	  ch.insert(g[n][j]);
	}
      }
    }
    
    if(k==0)cout<<"no"<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
int n;
int color[MAX];
vector<int> v[MAX];
void b(int s, int t){
	stack<int> S;
	S.push(s);
	int tp;
	color[s] = t;
	while (!S.empty()){
		int tp = S.top(); S.pop();
		for (int i = 0; i < v[tp].size(); i++){
			if (color[v[tp][i]] == MAX){
				color[v[tp][i]] = t;
				S.push(v[tp][i]);
			}
		}
	}
}
void a(){
	for (int i = 0; i < n; i++){
		color[i] = MAX;
	}
	int id = 0;
	for (int i = 0; i < n; i++){
		id++;
		if(color[i] == MAX)b(i,id);
	}
}
int main(){
	int m, s, t;
	int q;
	cin >> n >> m;
	for (int i = 0; i < m; i++){
		cin >> s >> t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	a();
	cin >> q;
	for (int i = 0; i < q; i++){
		cin >> s >> t;
		if (color[s] == color[t]) cout << "yes" << endl;
		else cout << "no" << endl;
 	}
	return 0;
}