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 <iostream>
#include <vector>
using namespace std;
typedef long long ll;
#define int ll

int rabel[100010], now_rabel;
bool is_search[100010];
vector<int> s, t;

void dfs(int p) {
  //cout << "now p = " << p << endl;
  //cout << "rabel[" << p << "] = " << now_rabel << endl;
  is_search[p] = true;
  rabel[p] = now_rabel;

  for (int i = 0; i < s.size(); i++) {
    if (s[i] > p) break;
    if (s[i] == p && is_search[t[i]] == false) {
      //cout << s[i] << " " << t[i] << endl;
      dfs(t[i]);
    }
  }
  //cout << "end p = " << p << endl;
}

signed main(void) {
  int n, m, o, p, q;

  cin >> n >> m;

  for (int i = 0; i < m; i++) {
    cin >> o >> p;
    s.push_back(o);
    t.push_back(p);
  }

  int k = 0, i;

  while(1) {
    dfs(k);

    for (i = 0; i < n; i++) {
      if (is_search[i] == false) {
        k = i;
        break;
      }
    }
    if(i == n) break;
    now_rabel = k;
    //cout << "rabel changed\n";
  }

  /*for (int i = 0; i < n; i++) {
    cout << i << " " << rabel[i] << endl;
  }*/

  cin >> q;

  for (int i = 0; i < q; i++) {
    cin >> o >> p;
    if(rabel[o] == rabel[p]) {
      cout << "yes\n";
    } else {
      cout << "no\n";
    }
  }
  return 0;
}

C++: 
#include<iostream>
#include<vector>
#include<cinttypes>
#include<numeric>


using ui32 = std::uint32_t;

class union_find {
public:
	using size_type = decltype(std::declval<std::vector<int>>().size());
private:
	std::vector<size_type> par;
	std::vector<size_type> size_;

public:
	union_find() :par{}, size_{} {}
	union_find(size_type s) :union_find{} {
		par.resize(s);
		std::iota(std::begin(par), std::end(par), 0);

		size_.resize(s, 1);
	}

	auto root(size_type index_)->size_type {
		if (par[index_] == index_)
			return
				par[index_];
		else
			return
				par[index_] = root(par[index_]);
	}

	auto size(size_type index_) {
		return size_[root(index_)];
	}

	auto same(size_type ai, size_type bi) {
		return root(ai) == root(bi);
	}

	auto unite(size_type ai, size_type bi) {
		auto ar = root(ai);
		auto br = root(bi);

		if (ar == br)
			return;

		const auto as = size(ar);
		const auto bs = size(br);

		if (as >= bs)
			std::swap(ar, br);

		par[br] = par[ar];

		if(as == bs)
			size_[ar] = size_[br] = as + bs + 1;

	}

};

int main() {

	ui32 n, m, q;

	std::cin >> n >> m;
	union_find uf(n);
	for (ui32 i{}; i < m; ++i) {
		ui32 s, t;
		std::cin >> s >> t;
		uf.unite(s, t);
	}

	std::cin >> q;
	for (ui32 i{}; i < q; ++i) {
		ui32 s, t; 
		std::cin >> s >> t;
		const auto ans = uf.same(s, t)?"yes":"no";
		std::cout << ans << "\n";
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<cstring>
#include<cstdio>
using namespace std;
const int MAX=100005;
vector<int> G[MAX];
bool vis[MAX];
int group[MAX];
int n,m,number=0;
void dfs(int u){
	group[u]=number;
	vis[u]=1;
	for(unsigned int i=0;i<G[u].size();i++){
		if(!vis[G[u][i]])dfs(G[u][i]);
	}
}
int main(){
	int q;
	cin>>n>>m;
	for(int i=0;i<m;i++){
		int u,v;
		cin>>u>>v;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	for(int i=0;i<n;i++){
			if(!vis[i]){
				dfs(i);
				number++;
			}
		}
	cin>>q;
	for(int i=0;i<q;i++){
		int u,v;
		cin>>u>>v;
		printf("%s\n",((group[u]==group[v])?"yes":"no"));
	}
}

C++: #include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#define N 100000
using namespace std;

int color[N];
vector<int> G[N];
queue<int> Q;
int n;

void bfs(int s,int c) {
	Q.push(s);
	color[s] = c;
	while (!Q.empty()) {
		for (unsigned int it = 0;it < G[Q.front()].size();it++)
			if (color[G[Q.front()][it]] == 0){
				Q.push(G[Q.front()][it]);
				color[G[Q.front()][it]] = c;
		    }
		Q.pop();
	 }
}

void Color() {
	int c = 0;
	for(int i=0;i<n;i++)
	if(color[i]==0) bfs(i, ++c);
}

int main() {
	int m, q;
	cin >> n >> m;
	for (int i = 0;i < m;i++) {
		int u, v;
		cin >> u >> v;
		G[u].push_back(v);
	}

	Color();

	cin >> q;
	for (int i = 0;i < q;i++) {
		int u, v;
		cin >> u >> v;
		if (color[u] == color[v] && color[u] != 0)
			cout << "yes" << endl;
		else
			cout << "no"<<endl;
	}
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<utility>
#include<numeric>
#include<vector>
#include<map>
#include<set>
#include<tuple>
#include<stack>
#include<queue>
#include<functional>
#include<iterator>
#include<cmath>

using namespace std;

typedef pair<int,int> P;


const int max_n = 1e5;

int par[max_n];
int rnk[max_n];

void init(int n){
	for(int i=0; i<n; i++){
		par[i] = i;
		rnk[i] = 0;
	}
}

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

void unite(int x, int y){
	x = find_root(x);
	y = find_root(y);
	if(x == y) return;

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

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


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

	init(n);

	int s,t;
	for(int i=0;i<m;i++){
		cin >> s >> t;
		unite(s,t);
	}

	int q;
	cin >> 	q;
	for(int i=0;i<q;i++){
		cin >> s >> t;
		if(same(s,t)) cout << "yes\n";
		else			cout << "no\n";
	}

	return 0;
}