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>

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);
      }
    }
  }
}

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 (void) {
  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);
  }

  assignColor();

  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 <bits/stdc++.h>
using namespace std;

#define NIL -1

void dfs(int r, int id, vector<vector<int>> &G, vector<int> &color) {
    stack<int> S;
    S.push(r);

    color[r] = id;
    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] = id;
                S.push(v);
            }
        }
    }
}

void assignColor(vector<vector<int>> &G, vector<int> &color) {
    int id = 1;

    for (int i = 0; i < G.size(); i++)
        color[i] = NIL;

    for (int u = 0; u < G.size(); u++) {
        if (color[u] == NIL) {
            dfs(u, id, G, color);
            id++;
        }
    }
}

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

    vector<vector<int>> G(n);
    vector<int> color(n);

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

    // グループ分け
    assignColor(G, color);

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

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1LL << 60;
const ll MOD = 1000000007;

int N, M;
int cnt = 0;
vector<vector<int>> G;

vector<int> seen;
void dfs(int v) {
    seen[v] = cnt;

    for (auto nv : G[v]) {
        if (seen[nv] != -1) continue;

        dfs(nv);
    }
}

int main() {
    cin >> N >> M;
    G.resize(N);
    seen.assign(N, -1);
    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 v = 0; v < N; v++) {
        if (seen[v] != -1) continue;

        dfs(v);
        cnt++;
    }

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

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

#define MAX_N 100000
#define MAX_M 100000

vector<int> G[MAX_N];

int main(void){
    int n, m;
    scanf("%d %d\n", &n, &m);
    for(int i = 0; i < m; i++){
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(b);
        G[b].push_back(a);
    }

    int q;
    scanf("%d", &q);
    for(int i = 0; i < q; i++){
        int a, b;
        scanf("%d %d", &a, &b);

        for(int j = 0; j < G[a].size(); j++){
            if(G[a][j] == b){
                printf("yes\n");
                break;
            }
            if(j == G[a].size() - 1){
                printf("no\n");
            }
        }
    }
}

C++: #include <stdio.h>
#include <set>
#define MAX_USER (100000)

typedef std::set<long> Circle;

void merge_circle( Circle** circleinfo , long uid1 , long uid2 )
{
	Circle* src;
	Circle* dst;
	if( circleinfo[ uid1 ]->size() < circleinfo[ uid2 ]->size() )
	{
		src = circleinfo[ uid1 ];
		dst = circleinfo[ uid2 ];
	}
	else
	{
		src = circleinfo[ uid2 ];
		dst = circleinfo[ uid1 ];
	}

	Circle::const_iterator itr;
	for( itr = src->begin() ; itr != src->end() ; itr++ )
	{
		circleinfo[ *itr ] = dst;
		dst->insert( *itr );
	}
}

void add_member( Circle** circleinfo , long uid1 , long uid2 )
{
	if( circleinfo[ uid1 ] == 0 && circleinfo[ uid2 ] == 0 )
	{
		//create new circle
		Circle* entry = new Circle;
		entry->insert( uid1 );
		entry->insert( uid2 );

		circleinfo[ uid1 ] = entry;
		circleinfo[ uid2 ] = entry;
	}
	else if( circleinfo[ uid1 ] != 0 && circleinfo[ uid2 ] == 0 )
	{
		circleinfo[ uid1 ]->insert( uid2 );
		circleinfo[ uid2 ] = circleinfo[ uid1 ];
	}
	else if( circleinfo[ uid1 ] == 0 && circleinfo[ uid2 ] != 0 )
	{
		circleinfo[ uid2 ]->insert( uid1 );
		circleinfo[ uid1 ] = circleinfo[ uid2 ];
	}
	else
	{
		if( circleinfo[ uid1 ] != circleinfo[ uid2 ] )
		{
			merge_circle( circleinfo , uid1 , uid2 );
		}
	}
}

int main( int argc , char** argv )
{

	//read setting
	long user_count;
	long friendship_count;
	scanf( "%ld %ld" , &user_count , &friendship_count );

	//initialize
	Circle** user_info = new Circle*[ user_count ];
	for( long i = 0 ; i < user_count ; i++ )
	{
		user_info[ i ] = 0;
	}

	//read user friendship
	for( long i = 0 ; i < friendship_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		add_member( user_info , uid1 , uid2 );
	}

	//read number of question
	long question_count;
	scanf( "%ld" , &question_count );

	//process question
	for( long i = 0 ; i < question_count ; i++ )
	{
		long uid1;
		long uid2;
		scanf( "%ld %ld" , &uid1 , &uid2 );

		if( user_info[ uid1 ] == user_info[ uid2 ] && user_info[ uid1 ] != 0 )
		{
			printf( "yes\n" );
		}
		else
		{
			printf( "no\n" );
		}
	}

	delete[] user_info;
	return 0;
}