Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
#define MAX (int)1e5

vector<int> G[MAX];
queue<int> qu;

int main() {
	int n, m, q;
	int ind,tmp;
	cin >> n >> m;
	bool flag = 0;
	for (int i = 0; i < m; i++) {
		cin >> ind >> tmp;
		G[ind].push_back(tmp);
	}
	cin >> q;
	for (int i = 0; i < q; i++) {
		cin >> ind >> tmp;
		flag = 0;
		qu.push(ind);
		while (not qu.empty()) {
			int u = qu.front(); qu.pop();
			if (u == tmp) {
				flag = 1;
				break;
			}
			for (int j = 0; j < G[u].size(); j++) {
				qu.push(G[u][j]);
			}
		}
		if (flag) cout << "yes" << endl;
		else cout << "no" << endl;
	}
}

C++: #include<iostream>
using namespace std;
const int MAX = 100000;
int n, U[MAX];
void init()
{
	for (int i = 0; i < n; i++)
		U[i] = i;
}
int getAncestor(int v)
{
	if (U[v] == v)
		return v;
	else
	{
		U[v] = getAncestor(U[v]);
		return U[v];
	}
}
void merge(int s, int t)
{
	int a1 = getAncestor(s);
	int a2 = getAncestor(t);
	if (a1 != a2)
		U[a2] = a1;
}
int main()
{
	int m;
	cin >> n >> m;
	init();
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		merge(s, t);
	}
	int q;
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		int s, t;
		cin >> s >> t;
		cout << ((getAncestor(s) == getAncestor(t)) ? "yes" : "no") << endl;
	}
}

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;
}