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<vector>
#define N 100000
using namespace std;

vector<int> G[N];
/*
??£??\??????????????????????????°???????????¨??????????????£????????????????????????DFS??§????????????

 */
int labels[N];

void dfs_init(){
    int i;
    for(i=0;i<N; i++)labels[i]=0;
}

/*
  ?????°?????¨??????????£?
  ??§???????????????????????????
  stack???????????°??§???????????????
 */
bool dfs(int u, int v){
    if (u == v) return true;
    labels[u] = 1;
    int i,x;
    for(i=0; i<G[u].size(); i++){
	x = G[u][i];
	dfs(x,v);
    }
    return false;
}

void dfs2(int u){
    labels[u]=1;
    int i;
    for(i=0; i<G[u].size(); i++){
	if (labels[G[u][i]]==0) dfs2(G[u][i]);
    }
}


int main(void) {
    int n,m,i,q, u,v;
    scanf("%d %d",&n,&m);
    for(i=0;i<m;i++){
	scanf("%d %d",&u,&v);
	G[u].push_back(v);
	G[v].push_back(u);
    }

    
    scanf("%d",&q);
    for(i=0;i<q;i++){
	scanf("%d %d", &u, &v);
	dfs_init();
	dfs2(u);
	if(labels[u]>0 && labels[u]==labels[v])printf("yes\n");
	else 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;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>

#define MAX 100000

#define WHITE 0
#define GRAY 1
#define BLACK 2


using namespace std;

vector<int> G[MAX];
int graphc[MAX];
int color[MAX];
int colorCount;

void def(int o)
{
	int v;

	for (int i = 0; i < G[o].size(); i++) {

		v = G[o][i];
		if (color[v] == WHITE) {

			color[v] = GRAY;
			def(v);
		}
	}
	color[o] = BLACK;
	graphc[o] = colorCount;
}


int main(void)
{
	int n;
	int m;
	int s;
	int t;
	int q;


	cin >> n >> m;

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

	for (int i = 0; i < n; i++) {

		if (color[i] == WHITE) {
			colorCount++;
			def(i);
			
		}
	}


	for (int i = 0; i < n; i++) {
		cout << graphc[i] << endl;
	}

	cin >> q;

	for (int i = 0; i < q; i++) {

		cin >> s >> t;

		cout << ((graphc[s] == graphc[t]) ? "yes" : "no" )<< endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

vector<vector<int>> v;
vector<int> d;

int lx = 1;
void bfs(int x){
  queue<int> q;
  q.push(x);
  d[x] = lx;

  while(!q.empty()){
    int node = q.front();
    q.pop();

    for(int i=0; i<v[node].size(); ++i){
      if(d[v[node][i]] == 0){
         q.push(v[node][i]);
         d[v[node][i]] = lx;
       }
    }
  }
  ++lx;
}

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

  v.resize(n);
  d.resize(n);

  for(int i=0; i<m; ++i){
    int x, y; cin >> x >> y;
    v[x].push_back(y);
    v[y].push_back(x);
  }

  for(int i=0; i<n; ++i) if(d[i] == 0) bfs(i);

  int q; cin >> q;
  while(q--){
    int x, y; cin >> x >> y;
    if(d[x] == d[y]) cout << "yes" << endl;
    else cout << "no" << endl;
  }
}

C++: #include <cstdio>
#include <vector>
#include <cstring>
#include <cstdlib>

void numbering(int id, int *g, int num, std::vector<int> *a){
    int tmp;
    for(int i=0;i<a[id].size();i++){
        tmp = a[id][i];
        if(g[tmp])continue;
        g[tmp] = num;
        numbering(tmp, g, num, a);
    }
}

void grouping(std::vector<int> *a, int *g, int n){
    int num = 1;
    for(int i=0;i<n;i++){
        if(g[i])continue;
        g[num] = num;
        numbering(i,g,num,a);
        num++;
    }
}

int main(){
    int i, n, m, q, s, t;
    int *g;
    scanf("%d %d",&n,&m);
    g = (int *)malloc(sizeof(int)*n);
    memset(g, 0, sizeof(int)*n);
    std::vector<int> a[n];
    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        a[s].push_back(t);
        a[t].push_back(s);
    }
    scanf("%d",&q);
    grouping(a,g,n);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(g[s]==g[t])printf("yes\n");
        else printf("no\n");
    }
    return 0;
}