Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: #include<iostream>
#include<vector>
#include<stack>
#include<cstdio>
using namespace std;
static const int MAX = 1000000;
static const int NIL = -1;

int n;
vector<int> G[MAX];     //頂点数を1000000とする
                        //隣接リスト
int color[MAX];

void dfs( int r, int c ) {
    stack<int> S;
    S.push(r);          //始点rをスタックに追加
    color[r] = c;       //色をいれる
    while ( !S.empty() ) {
        int u = S.top();
        S.pop();        //スタックから頂点uを取り出し訪問
        for ( int i = 0; i < G[u].size(); ++i ) {
            int v = G[u][i];
            //頂点uに隣接する頂点vを探索
            if ( color[v] == NIL ) {
                color[v] = c;
                S.push(v);//id(色)は変わらない
            }
        }
    }
}

void assignColor() {
    int id = 1;             //全てにNIL
    for ( int i = 0; i < n; ++i ) color[i] = NIL;
    for ( int u = 0; u < n; ++u ) {
        if ( color[u] == NIL ) dfs( u , id++ ); //id(色)にかぶりがないように
    }
}

int main() {
    int s, t, m, q;

    scanf("%d %d",&n,&m);

    for ( int i = 0; i < m; ++i ) {
        scanf("%d %d",&s,&t);
        G[s].push_back(t);  // s → tへ辺
        G[t].push_back(s);  // t → sへ辺
    }

    assignColor();

    scanf("%d",&q);

    for ( int i = 0; i < q; ++i ) {
        scanf("%d %d",&s,&t);
        if ( color[s] == color[t] ) {
            puts("yes");
        } else {
            puts("no");
        }
    }

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#define Lens 1005
#define Nil -1

using namespace std;
int n, m, q;
queue<int> Q;
vector<int> A[Lens];
int c[Lens], d[Lens];
int way[Lens][Lens];

void bns(int k, int v)
{
	Q.push(k);
	c[k] = v;
	while (!Q.empty())
	{
		k = Q.front();
		Q.pop();
		c[k] = v;
		for (int i = 0; i < A[k].size(); i++)
		{
			int tmp = A[k][i];
			if (c[tmp] == Nil)
			{
				Q.push(tmp);
			}
		}
	}
}

int main()
{
	int v = 1;
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		c[s] = c[t] = Nil;
		A[s].push_back(t);
		A[t].push_back(s);
	}
	for (int i = 0; i < n; i++)
	{
		if (c[i] == Nil)
		{
			bns(i, v);
			v++;
		}

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

		if (c[s] == c[t]&&c[s]!=Nil&&c[s]!=0)
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}
	return 0;
}

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

using namespace std;
struct user {
    user() {};
    user(int i) : id {i}, fs {}, group {-1} {};
    int id;
    vector<int> fs;
    int group;
};

void add_friends(user *us, int x, int y){
    us[x].fs.push_back(y);
    us[y].fs.push_back(x);
}

void dfs(user* us, int id, int g){
    if(us[id].group == g){
        return;
    }
    us[id].group = g;
    vector<int> fs = us[id].fs;
    for(auto x : fs){
        dfs(us, x, g);
    }
}

void make_group(user* us, int n){
    int g = 0;
    for(int i = 0; i < n; ++i){
        if(us[i].group < 0){
            dfs(us, i, g);
            ++g;
        }
    }
}

int main(){
    int n, m;
    cin >> n >> m;
    user us[n];
    for(int i = 0; i < n; ++i){
        us[i] = user(i);
    }
    for(int i = 0; i < m; ++i){
        int a, b;
        cin >> a >> b;
        add_friends(us, a, b);
    }
    make_group(us, n);
    int q;
    cin >> q;
    for(int i = 0; i < q; ++ i){
        int a, b;
        cin >> a >> b;
        if(us[a].group == us[b].group){
            cout << "yes" << endl;
        } else {
            cout << "no" << endl;
        }
    }
}

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

int main(){
	int n,m,q,i,j;
	int s,t;
	vector<int> L(100005,-1);
	cin >> n >> m;
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	for (i=0;i<m;i++){
		cin >> s >> t ;
		if (L[s]!=L[t]){
			int a=L[t];
			for (j=0;j<n;j++){
				if (L[j]==a){
					L[j]=L[s];
				}
			}
		}
	}
	
	cin >> q;
	for (i=0;i<q;i++){
		cin >> s >> t;
		if (L[s]==L[t]){
			cout << "yes" <<endl;
		}else{
			cout << "no" <<endl;
		}
	}
	
	for (i=0;i<n;i++){
		cout << L[i] << endl;
	} 
	
	return 0;
}

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

vector<int> *v;
int *color;
int n;

void dfs(int i, int c){
        if(color[i]==c) return;
        color[i]=c;
        for(int j=0;j<v[i].size();j++)
                dfs(v[i][j], c);
}

void assignColor(){
        int c = 1;
        for(int i=0;i<n;i++){
                if(color[i]!=0) continue;
                dfs(i,c);
                c++;
        }

}

int main(){
        int m,q,a,b;
        cin>>n>>m;
        v = new vector<int>[n];
        color = new int[n];
        for(int i=0;i<m;i++){
                cin>>a>>b;
                v[a].emplace_back(b);
                v[b].emplace_back(a);
        }
        for(int i=0;i<n;i++) color[i] = 0;

        assignColor();

        cin>>q;
        for(int i=0;i<q;i++){
                cin>>a>>b;
                if(color[a]==color[b]) cout<<"yes"<<endl;
                else cout<<"no"<<endl;
        }

        return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

vector<int> g[100000];
int c[100000],n;


void dfs(int r,int a){
  stack<int> s;
  s.push(r);
  c[r]=a;
  while(!s.empty()){
    int u=s.top();
    s.pop();
    for(int i=0;i<g[u].size();i++){
      int v=g[u][i];
      if(c[v]==-1){
	c[v]=a;
	s.push(v);
      }
    }
  }
}

void color(){
  int id=1;
  for(int i=0;i<n;i++) c[i]=-1;
  for(int i=0;i<n;i++){
    if(c[i]==-1) dfs(i,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);
  }
  color();
  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> using namespace std; const int N = 100000; int A[N][N] = {{0}}; int n; bool dfs(int s, int t) {     if (A[s][t] == 1) {         return true;     }     for (int i = 0; i < n; ++i) {         if (i != t && A[s][i] != 0) {             if (dfs(i, t)) {                 return true;             }         }     }     return false; } int main() {     int m;     cin >> n >> m;     for (int i = 0; i < m; ++i) {         int s, t;         cin >> s >> t;         A[s][t] = 1;     }     int q;     cin >> q;     for (int j = 0; j < q; ++j) {         int x, y;         cin >> x >> y;         if (dfs(x, y)) {             cout << "yes";         } else {             cout << "no";         }         cout << endl;     }     return 0; }