Go: package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX = 100000
	NIL = -1
)

var (
	n, m, q, s, t int
	G             [MAX][]int //連結リスト
	color         [MAX]int
)

func dfs(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

//幅優先探索で、頂点を色付け
func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			dfs(i, id)
		}
	}
}

func main() {
	sc.Split(bufio.ScanWords)
	n, m = nextInt(), nextInt()
	for i := 0; i < m; i++ {
		s, t = nextInt(), nextInt()
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)

	}
	assignColor()
	q = nextInt()
	for i := 0; i < q; i++ {
		s, t = nextInt(), nextInt()
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}

}

C++: #include <algorithm>
#include <iostream>
#include <string>
#include <vector>

class TUser
{
	std::vector<TUser*> FAccessible;
public:
	void AddFriend(TUser* Friend);
	bool IsAccesible(const TUser* Target)const;
};

void TUser::AddFriend(TUser* Friend)
{
	if(IsAccesible(Friend)) return;
	FAccessible.push_back(Friend);
	for(unsigned int i = 0; i < FAccessible.size(); ++i){
		FAccessible[i]->AddFriend(Friend);
		Friend->AddFriend(FAccessible[i]);
	}
}

bool TUser::IsAccesible(const TUser* Target)const
{
	return std::find(FAccessible.begin(), FAccessible.end(), Target) != FAccessible.end();
}

class TSns
{
	std::vector<TUser> FUsers;
public:
	TSns(int UserCount);
	
	void AddLink(int UserA, int UserB);
	std::string IsAccesible(int UserA, int UserB)const;
};

TSns::TSns(int UserCount)
: FUsers(UserCount)
{
}

void TSns::AddLink(int UserA, int UserB)
{
	FUsers[UserA].AddFriend(&FUsers[UserB]);
	FUsers[UserB].AddFriend(&FUsers[UserA]);
}

std::string TSns::IsAccesible(int UserA, int UserB)const
{
	if(FUsers[UserA].IsAccesible(&FUsers[UserB])) return "yes";
	return "no";
}

int main()
{
	int UserCount;
	std::cin >> UserCount;
	TSns Sns(UserCount);
	
	int LinkCount;
	std::cin >> LinkCount;
	for(int i = 0; i < LinkCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		Sns.AddLink(UserA, UserB);
	}
	
	int QuestionCount;
	std::cin >> QuestionCount;
	for(int i = 0; i < QuestionCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		std::cout << Sns.IsAccesible(UserA, UserB) << std::endl;
	}
	return 0;
}

C++: #include<stdio.h>
#include<vector>
#include<string>
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);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        visited.resize(n,false);
        string s1=(dfs2(s,t)?"yes":"no");
        string s2=(color[s]==color[t]?"yes":"no");
        if(s1!=s2)return 1;
        printf((color[s]==color[t]?"yes\n":"no\n"));
    }
    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.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 assignColor(){
  int i,u,id=1;
  for(i=0;i<n;i++) color[i] = NIL;
  for(u=0;u<n;u++){
    if(color[u]==NIL) bfs(u,id++);
  }
}

int main(){
  int i,s,t,m,q;
 cin >> n >> m;
  for(i=0;i<m;i++){
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }

  assignColor();

cin >> q;
  for(i=0;i<q;i++){
    cin >> s >> t;
    if(color[s]==color[t]){
 cout << ?¨yes?¨ <<endl;
    }
    else {
cout << ?¨no?¨ <<endl;
}
  }
  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){
                color[v]=c;
                S.push(v);
            }
        }
    }
}

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 s,t,m,q;

    cin>>n>>m;

    for(int i=0;i<m;i++){
        cin>>s>>t;
        G[s].push_back(t);
        G[s].push_back(s);
    }

    assignColor();

    cin>>q;

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

C++: #include <bits/stdc++.h>
using namespace std;
const int N = 1000000;
const int CRL = -1;
int v[N]={0};
void ketugou(int k,int l,int n){
	int x,mn;
	x = max(k,l);
	mn = min(k,l);
	for(int i=0;i<n;i++){
		if(v[i]==x)v[i]=mn;
	}
}

int main(){
	int n,m,q;
	memset(v, CRL, sizeof(v));
	cin >> n >> m;
	for(int i=0;i<m;i++){
		int k,l;
		cin >> k >> l;
		if(v[k]==CRL && v[l]==CRL){
			v[k] = v[l] = min(k,l);
		}else if(v[k]!=CRL && v[l]!=CRL){
			ketugou(k,l,n);
		}else if(v[k]==CRL){
			v[k]=v[l];
		}else{
			v[l]=v[k];
		}
	}
	cin >> q;
	for(int i=0;i<q;i++){
		int k,l;
		cin >> k >> l;
		if(v[k]==v[l])cout << "yes" << endl;
		else cout << "no" << endl;
	}
    return 0;
}