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 <stdio.h>
#include <algorithm>
#include <queue>

using namespace std;

struct Info{
	Info(){s = t = -1;}
	Info(int tmp_s,int tmp_t){
		s = tmp_s;
		t = tmp_t;
	}
	int s;
	int t;
};

class Relation{
public:
	Relation(int tmp_n,int tmp_m){
		n = tmp_n;
		m = tmp_m;
		global = new Info[m];
		each = new int*[n];
		each_index = new int[n];
		num_of_each = new int[n];
		went = new int[n];
		for(int i=0;i<n;i++){
			each_index[i] = 0;
			num_of_each[i] = 0;
			went[i] = 0;
		}
		global_index = 0;
	}

	void push(int s,int t){
		global[global_index++] = Info(s,t);
		num_of_each[s]++;
		num_of_each[t]++;
	}

	void allocate(){
		for(int i=0;i<n;i++){
			if(num_of_each[i] > 0){
				each[i] = new int[num_of_each[i]];
			}
		}
		Info tmp;
		for(int i=0;i<m;i++){
			tmp = global[i];
			each[tmp.s][each_index[tmp.s]++] = tmp.t;
			each[tmp.t][each_index[tmp.t]++] = tmp.s;
		}
	}


	void recursive(int s,int t,bool& FLG){
		went[s] = 1;
		for(int i=0;i<num_of_each[s];i++){
			if(each[s][i] == t){
				FLG = true;
				return;
			}
			else if(went[each[s][i]] == 0){
				recursive(each[s][i],t,FLG);
			}
		}
	}

	bool canAccsess(int s,int t){
		for(int i=0;i<n;i++)went[i]=0;
		bool FLG =false;
		recursive(s,t,FLG);
		if(FLG){
			return true;
		}
		else{
			return false;
		}
	}

private:
	Info* global;
	int** each;
	int* each_index;
	int* num_of_each;
	int global_index,n,m;
	int* went;
};

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

	Relation relation(n,m);
	for(int i=0;i<m;i++){
		scanf("%d %d",&s,&t);
		relation.push(s,t);
	}
	relation.allocate();
	scanf("%d",&q);
	for(int i=0;i<q;i++){
		scanf("%d %d",&s,&t);
		if(relation.canAccsess(s,t)){
			printf("yes\n");
		}else{
			printf("no\n");
		}
	}
    return 0;
}

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

int main(){
	int n,m,q,i,j;
	int s,t;
	vector<int> L(100005,-1);
	cin >> n >> m;
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	for (i=0;i<m;i++){
		cin >> s >> t ;
		if (L[s]!=L[t]){
			int a=L[t];
			for (j=0;j<n;j++){
				if (L[j]==a){
					L[j]=L[s];
				}
			}
		}
	}
	
	cin >> q;
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (L[s]==L[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	
	for (i=0;i<n;i++){
		cout << L[i] << endl;
	} 
	
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int INF = 1e9;

vector<vector<int> > g;
vector<int> ids;

void rec(int v, int id)
{
  int n = g[v].size();
  ids[v] = id;
  for (int i = 0; i < n; ++i) {
    if (ids[g[v][i]] == -1) {
      rec(g[v][i], id);
    }
  }
}

int main()
{
  int n, m;
  fscanf(stdin, "%d %d", &n, &m);
  g = vector<vector<int> >(n);
  ids = vector<int>(n, -1);
  for (int i = 0; i < m; ++i) {
    int s, t;
    fscanf(stdin, "%d %d", &s, &t);
    g[s].push_back(t);
    g[t].push_back(s);
  }
  int id = 0;
  for (int i = 0; i < n; ++i) {
    if (ids[i] == -1) {
      rec(i, id);
      ++id;
    }
  }
  int q;
  fscanf(stdin, "%d", &q);
  for (int i = 0; i < q; ++i) {
    int s, t;
    fscanf(stdin, "%d %d", &s, &t);
    fprintf(stdout, "%s\n", ids[s] == ids[t] ? "yes" : "no");
  }
  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define MAX 100010

class Union_Find{
public:
  int par[MAX],rank[MAX],size[MAX],gnum;
  Union_Find(int N){
    gnum = N;
    for(int i = 0 ; i < N ; i++){
      par[i] = i;
      rank[i] = 0;
      size[i] = 1;
    }
  }

  int find(int x){
    if(par[x] == x){
      return x;
    }
    return par[x] = find(par[x]);
  }

  void unite(int x,int y){
    x = find(x);
    y = find(y);
    if(x == y){ return; }
    if(rank[x] < rank[y]){
      par[x] = y;
      size[y] += size[x];
    }else{
      par[y] = x;
      size[x] += size[y];
      if(rank[x] == rank[y]){
        rank[x]++;
      }
    }
    gnum--;
  }

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

  int getSize(int x){
    return size[find(x)];
  }

  int groups(){
    return gnum;
  }
};

int main(){
  int N,M,Q,a,b;
  cin >> N >> M;
  Union_Find uf(N);
  for(int i = 0 ; i < M ; i++){
    cin >> a >> b;
    uf.unite(a,b);
  }
  cin >> Q;
  while(Q--){
    cin >> a >> b;
    cout << (uf.same(a,b) ? "yes" : "no") << endl;
  }
  return 0;
}