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 <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() {
  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++: // http://hfuji.hatenablog.jp/entry/2015/12/09/175721

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;
vector<int> par;
vector<int> rnk; // ??±???

void init(int n) {
  par = vector<int>(n);
  rnk = vector<int>(n);
  REP(i, n) {
    par[i] = i;
    rnk[i] = 0;
  }
}
int root(int key) {
  if (par[key] == key) return key;
  return root(par[key]);
}
int same(int a, int b) {
  return root(a) == root(b);
}
void unite(int a, int b) {
  int x = root(a);
  int y = root(b);
  if (x == y) return;

  if (rnk[x] < rnk[y]) {
    par[x] = y;
  } else {
    par[y] = x;
    if (rnk[x] == rnk[y]) rnk[x]++;
  }
}

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

  init(n);

  REP(_, m) {
    int a, b;
    // cin >> a >> b;
    scanf("%d %d", &a, &b);
    unite(a, b);
  }
  int q;
  cin >> q;
  REP(_, q) {
    int a, b;
    // cin >> a >> b;
    scanf("%d %d", &a, &b);
    if (same(a, b)) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define MAX 1001001
#define NIL -1

/*
  疎なグラフ(連結成分が少ないグラフ)では、隣接行列を使うのはメモリefficientではない。
  ->隣接リストを用いて各ノードの関係を表す

  連結成分を求めるには、未訪問のノードを始点としてDFSを行う。
  この探索を行うごとに、各点に異なるIDを割り振ることで、どのグループに属するかを判定する。
*/

int n;
vector<int> G[MAX]; //頂点数がMAXまで格納できる隣接リスト(中身は配列)
int color[MAX]; //

void dfs_colorAssign(int start, int group_id) {
  stack<int> s;
  s.push(start);
  color[start] = group_id;

  while(!s.empty()) {
    int now = s.top(); s.pop();

    for (int i = 0; i < G[now].size(); i++) {
      int v = G[now][i];
      if (color[v] == NIL) {
        color[v] = group_id;
        s.push(v);
      }
    }
  }
}

void assign_color() {
  int id = 1;
  for (int i = 0; i < n; i++) color[i] = NIL; //color配列を初期化
  //未訪問の頂点はidがNILになる
  for (int i = 0; i < n; i++) {
    if (color[i] == NIL) dfs_colorAssign(i, id);
    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); // 互いの隣接リストに相手を追加
    G[t].push_back(s);
  }

  assign_color();

  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<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int NIL = -1;
static const int MAX = 100000;

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