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>
using namespace std;

bool DFS(const vector<vector<int> >& G,
         vector<bool>& is_visited, int a, int b, int i) {
    if (a == b) return true;
    if (i >= G[a].size()) return false;
    if (!is_visited[G[a][i]]) {
        is_visited[G[a][i]] = true;
        return DFS(G, is_visited, G[a][i], b, 0);
    }
    return DFS(G, is_visited, a, b, i + 1);
}

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

    vector<vector<int> > G(n);
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
// 
// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }



    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        vector<bool> is_visited(n, false);
        if (DFS(G, is_visited, a, b, 0)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include <vector>
#include <iostream>
using namespace std;
int n, m, q, x, y, t; int group[111111]; vector<int> f[111111];
int main() {
	scanf("%d%d", &n, &m);
	for(int i = 0; i < n; i++) group[i] = i, f[i].push_back(i);
	for(int i = 0; i < m; i++) {
		scanf("%d%d", &x, &y);
		if(group[x] == group[y]) continue;
		x = group[x], y = group[y];
		if(f[y].size() > f[x].size()) swap(x, y);
		t = f[y].size();
		for(int j = 0; j < t; j++) {
			group[f[y].back()] = group[x];
			f[x].push_back(f[y].back());
			f[y].pop_back();
		}
	}
	scanf("%d", &q);
	for(int i = 0; i < q; i++) {
		scanf("%d%d", &x, &y);
		printf("%s\n", group[x] == group[y] ? "yes" : "no");
	}
	return 0;
}

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

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();
        for(int i=0; i<G[u].size(); i++){
            int v = G[u][i];
            if(color[v] == NIL){
                S.push(v);
                color[v] = c;
                // cout << color[v] << endl;
            }
        }
    }
}
void assignColor(){
    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 m, u, v, q;
    cin >> n >> m;
    for(int i=0; i<m; i++){
        cin >> u >> v;
        G[u].push_back(v);
        G[v].push_back(u);
    }

    assignColor();
    
    cin >> q;
    for(int i=0; i<q; i++){
        cin >> u >> v;
        cout << color[u] << color[v] << endl;
        if(color[u] == color[v]) cout << "yes\n";
        else cout << "no\n";
    }

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
//#define ll long long
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
#define rep(i, n) REP(i, 0, n)
#define rep_rev(i, n) for (int (i) = (int)(n) - 1 ; (i) >= 0 ; --(i))
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
#define all(x) (x).begin(),(x).end()
ll t1,t2;
const ll mod = 1000000007;
const int INF = 1e9;
const ll INFLONG = 1e18;
void swap(ll *x,ll *y){
  ll tmp;
  tmp = *x;
  *x = *y;
  *y = tmp;
}
vector<ll> kinds(100000,-1);
vector<ll> vec[100000];
void dfs(ll k,ll num){
  if(kinds[k] != -1){
    return;
  }
  kinds[k] = num;
  for(auto itr:vec[k]){
    dfs(itr,num);
  }
}
int main(){
  ll n,m;
  cin >> n >> m;
  rep(i,m){
    cin >> t1 >> t2;
    vec[t1].push_back(t2);
    vec[t2].push_back(t1);
  }
  rep(i,n){
    dfs(i,i);
  }
  ll q;
  cin >> q;
  rep(i,q){
    cin >> t1 >> t2;
    if(kinds[t1] == kinds[t2]){
      cout << "yes" << endl;
    }else{
      cout << "no" << endl;
    }
  }
  return 0;
}

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

vector<int> list[100000];
int num[100000];
int n,m;

void bfs(int s,int sign){

  queue<int> Q;
  Q.push(s);

  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(num[temp]==-1){ //未訪問なら
        Q.push(temp); num[temp]=sign;
      }
    }
  }
}
int main(){

  cin>>n>>m;

  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  fill(num,num+100000,-1);
  int q; cin>>q;

  int sign=0;
  for(int i=0;i<n;i++){
    if(num[i]==-1){
      bfs(i,sign++);
    }
  }
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(num[s]==num[t] && (num[s]!=-1 || num[t]!=-1)){
      cout<<"yes\n";
    }else{
      cout<<"no\n";
    }
  }

}