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<cstdio>
#include<vector>
#include<algorithm>
#include<utility>
#include<numeric>
#include<iostream>
#include<array>
#include<string>
#include<sstream>
#include<stack>
#include<queue>
#include<list>
#define _USE_MATH_DEFINES

#include<math.h>
#include<map>

#define SENTINEL 1000000001

#define min(a,b) (a)>(b)?(b):(a)
#define max(a,b) (a)>(b)?(a):(b)

using namespace std;

int from[100000];
int to[100000];

bool judge(int f, int t,int n)
{
	bool isFriend = false;
	for (int i = 0; i < n; i++)
	{
		if (from[i] == f)
		{
			if (to[i] == t)
			{
				isFriend = true;
			}
			else
			{
				isFriend = judge(to[i], t, n);
			}
			if (isFriend)
			{
				break;
			}
		}
	}
	return isFriend;
}

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

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

		from[i] = f;
		to[i] = t;
	}

	int q;
	cin >> q;

	for (int i = 0; i < q; i++)
	{
		int f, t;
		cin >> f >> t;

		printf(judge(f, t, n) ? "yes\n" : "no\n");
	}
	return 0;
}

C++: //
//
//  ad-algoD.cpp - created by us162022
//
#include <iostream>
using namespace std;
int find(int join[],int x){
  if(x==join[x])
    return x;

  return find(join,join[x]);
}
int main(int argc, char *argv[])
{
  int n,m,join[100000],num[100000],s,t;
  cin >> n >> m;

  for(int i=0; i<n; i++){
    join[i] = i;
    num[i] = 0;
  }

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

    if(s!=t){
      if(num[s] < num[t])
	join[s] = t;
      
      else{
	join[t]=s;
	if(num[s]==num[t])
	  num[s]++;
      }

    }
  }

  int q;
  cin >> q;

  for(int i=0; i<q; i++){
    cin >> s >> t;

    if(find(join,s)==find(join,t))
      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 NTL = -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]==NTL){
      color[v]=c;
      S.push(v);
      }
    }
  }
}

void assigncolor() {
  int id=1;
  for(int i=0;i<n;i++) color[i]=NTL;
  for(int u =0;u<n;u++){
    if(color[u]==NTL)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 <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <vector>
#include <stack>
#include <queue>
#define rep(i, n) for(int i = 0; i < n; i++)
using namespace std;
typedef long long ll;
ll mod = 1000000007;

const int MAX = 100000;
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();
        rep(i, G[u].size()) {
            int v = G[u][i];
            if(color[v] == NIL) {
                color[v] = c;
                S.push(v);
            }
        }
    }
}

void assignColor() {
    int id = 1;
    rep(i, n) {
        color[i] = NIL;
    }
    rep(u, n) {
        if(color[u] == NIL) {
            dfs(u, id++);
        }
    }
}
 
int main() {
    int s, t, m, q;

    cin >> n >> m;

    rep(i, m) {
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    assignColor();

    cin >> q;

    rep(i, q) {
        cin >> s >> t;
        if(color[s] == color[t]) {
            cout << "yes" << endl;
        }
        else {
            cout << "no" << endl;
        }
    }
    
    return 0;
}

C++: #include <cstdint>
#include <vector>

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[i].connections.size(); i++) {
      colorize(graph[i].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection()
{
  for (uint32_t i = 0; i < GRAPH_SIZE; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 0;
  for (uint32_t i = 0; GRAPH_SIZE; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
  }

  check_connection();

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}