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++: /**
 */

/*
 * test case 1
 2 1 1 2 1 1 2  
 test case 2
 4 4 1 2 1 3 2 4 3 4 1 1 2   
 */


#include <iostream>
#include <vector>
#include <queue>
using namespace std;
vector< vector<int> > rel;
vector<bool> visited;
int n, m, q;
int dest = 0;


bool fre1(int j) 
{
	for (int i=0;i<rel[j].size();i++)
	{
		int kk = rel[j][i];
		if (kk==dest) return true;
		if (visited[kk])continue;
		visited[kk]=true;
		if(fre1(kk))return true;
	}
	return false;
}

/**
 * preserve a priority que of nodes with the most connections. 
 * if there is a node with only 2 connections go look for the other one.
 */

priority_queue< pair<int, int> > pq;


bool fre3(int start) 
{
	for (int i=0;i<rel[start].size();i++)
	{
		int cand = rel[start][i];
		if (cand==dest) return true;
		if (visited[cand])continue;
		visited[cand]=true;
		int point = rel[cand].size();
		if (point == 1) continue;
		if (point == 2) {
			if (fre3(cand)) return true;
		} else {
			pq.push(pair<int, int>(point, cand));
		}
	}
	return false;
}


bool fre2(int start) 
{
	pq.push(pair<int,int>(0, start));
	while (pq.size())
	{
		pair<int, int> p = pq.top();
		pq.pop();
		start = p.second;
		if (fre3(start)) return true;
	}
	return false;
}


int main()
{
	cin >> n;
	rel.resize(n);
	cin >> m;
	for (int i=1;i<=m;i++){
		int j, k;
		cin >> j >> k;
		rel[j].push_back(k);
		rel[k].push_back(j);
	}

	cin >> q;
	for (int i=1;i<=q;i++){
		int start;
		cin >> start >> dest;
		visited.clear();
		visited.resize(n, false);
		cout << (fre2(start) ? "yes" : "no") << endl;
		while (pq.size()) pq.pop(); // forgot this.
	}

	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <queue>

#define MAX 100000


using namespace std;


int main(void)
{
	int n;
	int m;
	int s;
	int t;
	int q;
	int type = 1;

	int gcol[MAX];

	cin >> n >> m;

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

		if (gcol[s] != 0) {
			gcol[t] = gcol[s];
		}
		else if (gcol[t] != 0) {
			gcol[s] = gcol[t];
		}
		else {
			gcol[s] = gcol[t] = type;
			type++;
		}
	}

	cin >> q;

	for (int i = 0; i < q; i++) {
		cin >> s >> t;

		if (gcol[s] == gcol[t] && gcol[s] != 0) {
			cout << "yes";
		}
		else {
			cout << "no";
		}

		cout << endl;

	}

	return 0;
}

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

static const int MAX = 100000;
static 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 ) {
	color[v] = c;
	S.push(v);
      }
    }
  }
}

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);
  }

  int id = 1;
  
  for ( int i = 0; i < n; ++i) {
    color[i] = NIL; //preset
  }
  
  for ( int u = 0; u < n; ++u) {
    if ( color[u] == NIL ) {
      dfs(u,id);
      id++;
    }
  }
  
  scanf("%d", &q);
  for ( int i = 0; i < q; ++i) {
    scanf("%d %d", &s, &t);
    if ( color[s] == color[t] ) {
      printf("yes\n");
    } else {
      printf("no\n");
    }
  }

  return (0);
}

C++: #include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <map>
#include <set>
#include <queue>
#include <list>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
#define REP(i,a,b) for(int i=(a);i<(b);++i)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
long long gcd(long long a, long long b){return (b == 0 ? a : gcd(b, a%b));}
long long lcm(long long a, long long b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ld EPS=10e-8;
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
    for(auto i=begin(v); i != end(v); ++i){
        if(i !=begin(v)) os << ' ';
        os << *i;
    }
    return os;
}

vector<vector<ll>> V(100007);
ll chek[100007];

void dfs(ll num,ll T){
    chek[num]=T;
    rep(i,V[num].size()){
        if(chek[V[num][i]]==0){
            dfs(V[num][i],T);
        }
    }
}

int main(){
    ll N,M;cin >> N >> M;
    ll A,B,T=1;
    rep(i,M){
        cin >> A >> B;
        V[A].pb(B);
        V[B].pb(A);
    }
    rep(i,N){
        if(chek[i]==0){
            dfs(i,T);
            T++;
        }
    }
    ll Q;cin >> Q;
    rep(i,Q){
        cin >> A >> B;
        if(chek[A]==chek[B]){
            cout << "yes" << endl;
        }
        else{
            cout << "no" << endl;
        }
    }
}