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 <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>

using namespace std;

#define MAX_N 100000

vector<int> G[MAX_N];
vector<int> rG[MAX_N];
vector<int> vs;
bool used[MAX_N];
int cmp[MAX_N];
int V;

void add_edge(int from, int to) {
	G[from].push_back(to);
	rG[to].push_back(from);
}

void dfs(int v) {
	used[v] = true;
	for (int i = 0; i < G[v].size(); ++i)
		if (!used[G[v][i]])
			dfs(G[v][i]);
	vs.push_back(v);
}

void rdfs(int v, int k) {
	used[v] = true;
	cmp[v] = k;
	for (int i = 0; i < rG[v].size(); ++i)
		if (!used[rG[v][i]])
			rdfs(rG[v][i], k);
}

int scc() {
	fill_n(used, MAX_N, false);
	vs.clear();
	for (int v = 0; v < V; ++v)
		if (!used[v])
			dfs(v);
	fill_n(used, MAX_N, false);
	int k = 0;
	for (int i = vs.size() - 1; i >= 0; --i)
		if (!used[vs[i]])
			rdfs(vs[i], k++);
	return k;
}

int main() {
	int n, m;
	cin >> n >> m;
	V = n;
	for (int i = 0; i < m; ++i) {
		int s, t;
		cin >> s >> t;
		add_edge(s, t);
	}
	int k = scc();
	int q;
	cin >> q;
	for (int i = 0; i < q; ++i) {
		int s, t;
		cin >> s >> t;
		fill_n(used, MAX_N, false);
		dfs(s);
		if (used[t])
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;

int n;
int parent[100000];
int r[100000]; //rank

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

int find(int x){
  if(parent[x] == x) return x;
  else return parent[x] = find(parent[x]);
}

void unite(int x, int y){
  x = find(x);
  y = find(y);
  
  if(x == y) return ;
  
  if(r[x] < r[y]) parent[x] = y;
  else{
    parent[y] = x;
    if(r[x] == r[y]) r[x]++;
  }
}

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

int main(){
  
  int m, q, s, t;
  
  cin >> n >> m;
  init(n);
  for(int i = 0;i < m;i++){
    cin >> s >> t;
    unite(s, t);
  }
  
  cin >> q;
  for(int i = 0;i < q;i++){
    cin >> s >> t;
    if(same(s, t)) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  
  return 0;
}

C++: #include <iostream>
#include <array>
#include <vector>
#include <stack>
#include <queue>

const int nmax = 100005;
int n;
const int NIL = -1;

std::vector<int> adjlist[nmax];
std::array<int, nmax> group;

std::stack<int> stk;
std::array<int, nmax> state;

void init()
{
  group.fill(NIL);
  state.fill(0);
}

int next(int v)
{
  for (int i=0; i<adjlist[v].size(); ++i)
    {
      auto v_next = adjlist[v][i];
      if (state[v_next] == 0)
        return v_next;
    }
  return NIL;
}

void dfs_1v(int u, int group_id)
{
  stk.push(u);
  state[u] = 1;
  group[u] = group_id;

  while (!stk.empty())
    {
      auto v = stk.top();
      auto v_next = next(v);

      if (v_next != NIL)
        {
          stk.push(v_next);
          state[v_next] = 1;
          group[v_next] = group_id;
        }
      else
        {
          state[v] = 2;
          stk.pop();
        }
    }
}

void grouping()
{
  init();

  auto group_id = 0;
  for (int i=0; i<n; ++i)
    {
      if (state[i] == 0)
        {
          dfs_1v(i, group_id);
          group_id++;
        }
    }
}

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

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

      adjlist[s].push_back(t);
      adjlist[t].push_back(s);
    }

  grouping();

  int q;
  std::cin >> q;
  for (int i=0; i<q; ++i)
    {
      int s, t;
      std::cin >> s >> t;
      if (group[s] == group[t] && group[s] != NIL)
        std::cout << "yes\n";
      else
        std::cout << "no\n";
    }
}

C++: #include<iostream>
#include<list>
#include<iterator>
using namespace std;

class person
{
public:
	int id;
	bool Isdone = false;
	list <person*> lis;
	bool serch(person* Per)
	{
		Isdone = true;
		for(list<person*>::iterator temp=lis.begin();temp!=lis.end();++temp)
		{
			if ((*temp) == Per)return true;
			else if ((*temp)->Isdone == true)continue;
			else
			{
				if ((*temp)->serch(Per))return true;
			}
		}
		return false;
	}
};

person P[100001];

int main()
{
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < n; i++)P[i].id = i;
	for (int i = 0; i < m; i++)
	{
		int p1, p2;
		scanf_s("%d%d",&p1, &p2);
		P[p1].lis.push_back(&P[p2]);
		P[p2].lis.push_back(&P[p1]);
	}			 
	int q;
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		int p1, p2;
		scanf_s("%d%d", &p1, &p2);
		if (P[p1].serch(&P[p2]))
		{
			cout << "yes" << endl;
		}
		else
		{
			cout << "no" << endl;
		}
		for (int l = 0; l < n; l++)P[l].Isdone = false;
	}
	return 0;
}