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;
void numbering(int v, int k, vector<vector<int>>const&graph, vector<int>&id) {
	
	id[v] = k;
	//v????????????????????????
	//id??????????????°?????????????????????
	//k????????????????????????
	for (auto to : graph[v]) {
		//for(int i=0;i<graph[v].size();++i)
		
		if (id[to] != -1) {
			continue;
		}
		numbering(to, k, graph, id);
	}
}
int main() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>>graph(n);
	for (int i = 0;i < m;++i) {
		int u, v;
		cin >> u >> v;
		graph[u].push_back(v);
		graph[v].push_back(u);
	}
	vector<int>id(n, -1);
	for (int i = 0;i < n;i++) {
		if (id[i] == -1) {
			numbering(i, i, graph, id);
			//numbering(?????????????????????,?????????????????????,graph,id)
		}
	}
	int q;
	cin >> q;
	while (q--) {
		int u, v;
		cin >> u >> v;
		if (id[u] == id[v]) {
			cout <<"yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

}

C++: #include <stdio.h>

int m[100000] = {0};

void init() {
	int i;
	for ( i = 0; i < 100000; ++i) {
		m[i] = i;
	}
}

int find(int n) {
	if ( n == m[n]) {
		return n;
	}
	return m[n] = find(m[n]);
}

int friend (int x, int y) {
	if ( find(x) == find(y)) {
		return 1;
	} else {
		return 0;
	}
}

void unit (int x, int y) {
	x = find(x);
	y = find(y);
	
	if ( x == y ) {
		return ;
	}
	m[y] = x;
}

int main() {
	int n, s, t, u, v, i;
	init();
	scanf("%d", &n);
	scanf("%d", &s);
	
	for ( i = 0; i < s; ++i) {
		scanf("%d", &u);
		scanf("%d", &v);
		unit( u, v);
	}
	
	scanf("%d", &t);
	
	for ( i = 0; i < s; i++) {
		scanf("%d", &u);
		scanf("%d", &v);
		if ( friend( u, v) == 1) {
			printf("yes\n");
		} else {
			printf("no\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#define MAX 100000

using namespace std;

int main(){
  int a[MAX]={};
  int n,m; cin>>n>>m;
  int s,t;
  int group=1;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    if(a[s]==0 && a[t]==0){
      a[s]=a[t]=group;
      group++;
    }else if(a[s]==0){
      a[s]=a[t];
    }else if(a[t]==0){
      a[t]=a[s];
    }else{
      int tmp=a[t];
      a[t]=a[s];
      for(int j=0;j<i;j++){
        if(a[j]==tmp) a[j]=a[s];
      }
    }
  }

  int q; cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(a[s]==a[t]&&a[s]*a[t]!=0){
      cout<<"yes"<<endl;
    }else{
      cout<<"no"<<endl;
    }
  }

}

C++: #include<iostream>
#include<bits/stdc++.h>
using namespace std;
const int MAX=1e5+9;
int idx[MAX]={0};
void init(){
	int i;
	for(i=0;i<MAX;i++)
		idx[i]=i;
}
int findroot(int i){
	while(i!=idx[i])
		i=idx[i];
	return i;
}
void munion(int u ,int v){
	u=findroot(u);
	v=findroot(v);
	if(u!=v)
		idx[v]=u;
}
int main(){
	int i ,j ,n ,m;
	cin>>n>>m;
	init();
	while(m--){
		int x ,y;
		cin>>x>>y;
		munion(x ,y);
	}
	int q;
	cin>>q;
	while(q--){
		int  u ,v;
		cin>>u>>v;
		u=findroot(u);
		v=findroot(v);
		if(u==v)
			cout<<"Yes"<<"\n";
		else
			cout<<"No"<<"\n";
	}
}

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;
        }
    }
}

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() 
{
    ios::sync_with_stdio(false);
    
    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(t);
    }

    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;
}