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>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

C++: #include<iostream>
#include<vector>
#include<limits.h>
#include<stack>
#include<string>
using namespace std;

vector< vector<int> > L(100005);
int c[100005]={};
bool r;

void dfs (int v, int marker){
	if(c[v]!=0){
		r=false;
		return;
	}
	r=true;
	c[v]=marker;
	for (int i=0;i<L[v].size();i++){
		dfs(L[v][i],marker);
	}
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	int n,m,a,b,q,s,t;
	cin >> n >> m;
	
	for (int i=0;i<m;i++){
		cin >> a >> b;
		L[a].push_back(b);
	}
	
	int marker=1;
	for (int i=0;i<n;i++){
		dfs(i,marker);
		if (r) marker++;
	}
	
	
	for (int i=0;i<n;i++){
		cout << c[i] <<endl;
	}
	
	cin >> q;
	for (int i=0;i<q;i++){
		cin >> s >> t;
		if(c[s]==c[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
#include<queue>
using namespace std;
int inf = 1000000000;

class UF{
public:
  vector<int> u;
  vector<int> r;

  void init(int n){
    u.resize(n, 0);
    r.resize(n, 0);
    for(int i=0; i<n; i++) u[i] = i;
  }
  int root(int x){
    // if( u[x] == x ) return x;
    // else return root(u[x]);
    return u[x] == x ? x : u[x] = root(u[x]);
  }
  bool same(int x, int y){
    return root(x) == root(y);
  }
  void unite(int x, int y){
    x = root(x);
    y = root(y);
    if( x == y ) return;

    if( r[x] < r[y] ){
      u[x] = y;
    }else{
      u[y] = x;
      if( r[x] == r[y] ) r[x]++;
    }
  }
};

int main(void) {

  int n, m;
  cin >> n >> m;
  UF uf;
  uf.init(n);
  int s, t;
  for(int i=0; i<m; i++){
    scanf("%d %d", &s, &t);
    uf.unite(s, t);
  }
  int q;
  cin >> q;
  for(int i=0; i<q; i++){
    scanf("%d %d", &s, &t);
    cout << ( uf.same(s, t) ? "yes" : "no" ) << endl;
  }



  return 0;
}

// EOF

C++: #include <iostream>
#include <vector>
#include <unordered_set>
#include <algorithm>
//#include "../cxx-prettyprint/prettyprint.hpp"

std::vector<std::vector<int>> Adj;
std::unordered_set<int> nodes_visited;

bool is_reachable(int s, int t) {
    if (std::find(Adj[s].begin(), Adj[s].end(), t) != Adj[s].end()) {
        return true;
    } else if (nodes_visited.find(s) != nodes_visited.end()) {
        return false;
    } else {
        nodes_visited.insert(s);
        bool value = std::any_of(Adj[s].begin(), Adj[s].end(),
                                 [&](int next){return is_reachable(next, t);});
        return value;
    }
}

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

    Adj.assign(n, std::vector<int>());
    for (int i = 0; i < m; i++) {
        int s, t;
        std::cin >> s >> t;
        Adj[s].push_back(t);
        Adj[t].push_back(s);
    }

    int q;
    std::cin >> q;
    for (int i = 0; i < q; i ++) {
        int s, t;
        std::cin >> s >> t;
        std::cout << (is_reachable(s, t) ? "yes" : "no") << std::endl;
        nodes_visited.clear();
    }
}

C++: #include<iostream>
#include<vector>
#include<stack>
#define MAX 100000
#define NIL -1
using namespace std;

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 assign()
{
  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);
    }

  assign();

  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;
}