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++: #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;
}

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

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
bool dfs2(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs2(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
        g[t].push_back(s);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    visited.resize(n);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        for(int j=0;j<n;j++)visited[j]=false;
        string s1=(dfs2(s,t)?"yes":"no");
        cout<<s1<<endl;
    }
    return 0;
}