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<vector>
#include<iostream>
using namespace std;

#define MAX_N 100000
int par[MAX_N];//親の要素
int rank_[MAX_N];

//n要素で初期化
void init(int n)
{
	for (int i = 0; i < n; i++)
	{
		par[i] = i;
		rank_[i] = 0;
	}
}

//木の根を求める
int root(int x)
{
	if (par[x] == x)
	{
		return x;
	}
	else
	{
		return par[x] = root(par[x]);
	}
}

//xとyが同じ集合に属するか　否か
bool same(int x, int y)
{
	return root(x) == root(y);
}

//xとyの属する集合を併合
void unite(int x, int y)
{
	x = root(x);
	y = root(y);
	if (x == y)
	{
		return;
	}

	if (rank_[x] < rank_[y])
	{
		par[x] = y;
	}
	else
	{
		par[y] = x;
		if (rank_[x] == rank_[y])
		{
			rank_[x]++;
		}
	}


}

int main()
{
	int n;
	cin >> n;//頂点の数
	int m;
	cin >> m;//辺の数

	//初期化
	init(n);

	//木を作る
	for (int i = 0; i < m; i++)
	{
		int a, b;
		cin >> a >> b;
		if (same(a, b))
		{
			continue;
		}
		else
		{
			unite(a, b);
		}
	}

	int q;//クエリの数
	cin >> q;

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

	return 0;





}

C++: #include <iostream>
#include <stack>
#define N 100005


using namespace std;
int M[N][N];
int color[N];
int m, n;
int s, t, q;
int i, j;
int nt[N];
int next(int u){
	for(int v = nt[n]; v < n; v++){
		nt[u] = v + 1;
		if(M[u][v] && color[v] == 0) return v;
	}
	return -1;
}
int dfs(int s, int t){
	stack <int> S;
	S.push(s);
	color[s] = 1;
	while( !S.empty() ){
		int u = S.top();
		int v = next(u);
		if(v == t){
			return 1;
		}
		if(v != -1){
			if(color[v] == 0){
				color[v] = 1;
				S.push(v);
			}
		}
		else{
			S.pop();
			//color[u] = 1;
		}
	} 
	return 0; 
}
int main(){
	cin >> n >> m;
	for(i = 0; i < n; i++){
		color[i] = 0;
		for(j = 0; j < n; j++){
			M[i][j] = 0;
		}
	}
	for(i = 0; i < m; i++){
			cin >> s >> t;
			M[s][t] = M[t][s] = 1;
		
	}
	/*for(i = 0; i < n; i++){
		for(j = 0; j < n; j++){
			cout << M[i][j] << " ";
		}
		cout << endl;
	}*/
	cin >> q;
	for(i = 0; i < q; i++){
		cin >> s >> t;
		if(dfs(s, t)) 
			cout << "yes" << endl;
		else 
			cout << "no" << endl;
		for(j = 0; j < n; j++){
			color[j] = 0;
		}
	}
	
}

C++: #include<stdio.h>
#include<queue>
#include<vector>

#define MAX 100000

std::vector<int> G[MAX+1];
int n, m;

bool bfs(int src, int dest) {
    bool C[MAX];
    for (int i = 0; i < n; ++i) C[i] = false;

    std::queue<int> Q;
    Q.push(src);
    while(!Q.empty()) {
        int cur = Q.front();Q.pop();
        for (int i = 0; i < G[cur].size(); ++i) {
            int t = G[cur][i];
            if (C[t]) continue;
            if (t == dest) return true;
            Q.push(t);
            C[t] = true;
        }
    }

    return false;
}

int main() {
    scanf("%d %d", &n, &m);

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

    int q;
    scanf("%d", &q);
    for (int i = 1; i <= q; ++i) {
        int s,d;
        scanf("%d %d", &s, &d);
        bfs(s, d) ? printf("yes\n") : printf("no\n");
    }

    return 0;
}

C++: #include <iostream>
#include <cstring>
#include <cstdlib>
#include <sstream>
#include <stack>
#include <queue>
#include <list>
#include <stdio.h>
#include <algorithm>
#define MAX 100000
using namespace std;
typedef long long ll;
#define MAX 100000
vector<int> g[MAX];
int col[MAX];
void dfs(int s,int color)
{
	int v;
	col[s]=color;
	for(int i=0;i<g[s].size();i++)
	{
		v=g[s][i];
		if(col[v]==-1){
			dfs(v,color);
		}
	}
}
void init(int n)
{
	int id=0;
	for(int i=0;i<n;i++)
	{
		if(col[i]==-1){
			dfs(i,++id);
		}
	}
}
int main()
{	
	int n,m,num;
	int s,k;
	cin>>n>>m;
	for(int i=0;i<m;i++)
	{
		cin>>s>>k;
		g[s].push_back(k);
		g[k].push_back(s);
	}
	for(int i=0;i<n;i++)
	{
		col[i]=-1;
	}
	init(n);
	cin>>num;
	while(num--)
	{
		cin>>s>>k;
		if(col[s]==col[k]) cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int n, m;
vector< list<int> > v;
vector<bool> used;
int p[100000];
int r[100000];

int find(int x){
  if(p[x] == x) return x;
  else return p[x] = find(p[x]);
}
void unite(int x, int y){
  x = find(x);
  y = find(y);
  if(x == y) return;

  if(r[x] < r[y])
    p[x] = y;
  else{
    p[y] = x;
    if(r[x] == r[y]) r[x]++;
  }
}

bool same(int x, int y){
  return find(x) == find(y);
}

void dfs(int pos, int bgn){
  if(used[pos]) return;
  used[pos] = true;
  unite(pos, bgn);
  for(list<int>::iterator it = v[pos].begin(); it != v[pos].end(); it++){
    dfs(*it, bgn);
  }
}

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

  cin >> n >> m;
  v = vector< list<int> >(n, list<int>(0));
  used = vector<bool>(n, false);
  for(int i = 0; i < m; i++){
    int a, b; cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }

  for(int i = 0; i < n; i++){
    p[i] = i;
    r[i] = 0;
  }

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

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