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<algorithm>
#include<bitset>
#include<cassert>
#include<cfloat>
#include<climits>
#include<cmath>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>
#include<complex>
#include<list>
#include<cstdio>

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)


using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;




const int INF = 1e9 + 7;


/******************************************************************************************/


//繋げる方向を一方向にする
typedef struct union_find {

	vector<ll> pa;//親
	vector<ll> ra;//木の深さ
	vector<ll> siz;
	//n要素で初期化
	void init(ll n) {
		pa.resize(n);
		ra.resize(n);
		siz.resize(n);
		for (ll i = 0; i < n; i++) {
			pa[i] = i;/*各ノードに番号を振る,この時par[x]=xとなる時は木の根となる*/
			ra[i] = 0LL;/*各ノード自体の高さは0*/
			siz[i] = 1LL;
		}
	}
	//木の根を求める
	ll find(ll x) {
		if (pa[x] == x) {
			return x;/*根ならそのノードの番号を返す*/
		}
		else {
			return pa[x] = find(pa[x]);/*根でないならさらにノードの根を探す*/
		}
	}

	//xとyの属する集合を併合する
	void unite(ll x, ll y) {
		x = find(x);//xの根の番号を探す
		y = find(y);//yの根の番号を探す
		if (x == y) {//一致すればつながっている
			return;
		}
		pa[y] = x;
		siz[x] += siz[y];
	}

	//xとyが同じ集合に属するか判定
	bool same(ll x, ll y) {
		return find(x) == find(y);//同じ集合なら1、違うなら0が返る
	}
}UF;

int main() {

	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(10);

	
	int n, m, q;

	cin >> n >> m;

	UF tree;
	tree.init(n+10);

	for (int i = 0; i < m; i++)
	{
		int a, b;
		cin >> a >> b;
		if (a > b) {
			swap(a, b);
		}
		//b→a
		tree.unite(a, b);

	}

	cin >> q;

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


	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<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<n;i++)
using namespace std;

int par[100000],high[100000];
int find(int x){
	if(x==par[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(high[x]>high[y]){
		par[y]=x;
	}
	else{
		par[x]=y;
		if(high[x]==high[y]){
			high[y]++;
		}
	}
}
int main(){
	int n,m;cin>>n>>m;
	rep(i,n){
		par[i]=i;
	}
	rep(i,m){
		int s,t;cin>>s>>t;
		unite(s,t);
	}
	int q;cin>>q;
	rep(i,q){
		int s,t;cin>>s>>t;
		puts(find(s)==find(t)?"yes":"no");
	}
}