Go: // AOJ ALDS1_11_D: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_D

package main

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

var nocolor = -1

type graph struct {
	graph  [][]int
	colors []int
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

func newGraph(nodeNum int) *graph {
	colors := make([]int, nodeNum)
	g := make([][]int, nodeNum)
	for i := 0; i < nodeNum; i++ {
		g[i] = []int{}
		colors[i] = nocolor
	}

	return &graph{g, colors}
}

func constructGraph(sc *bufio.Scanner) *graph {
	usersNum := nextInt(sc)
	linkNum := nextInt(sc)

	g := newGraph(usersNum)
	for i := 0; i < linkNum; i++ {
		u := nextInt(sc) // node
		l := nextInt(sc) // link node
		// edge each other
		g.graph[u] = append(g.graph[u], l)
		g.graph[l] = append(g.graph[l], u)
	}
	return g
}

func (g *graph) dfs(r, color int) {
	g.colors[r] = color

	stack := list.New()
	stack.PushFront(r)

	for stack.Len() > 0 {
		v := stack.Remove(stack.Front()).(int)
		for _, u := range g.graph[v] {
			if g.colors[u] == nocolor {
				g.colors[u] = color
				stack.PushFront(u)
			}
		}
	}
}

func (g *graph) assignColor() {
	color := 1
	for u := 0; u < len(g.graph); u++ {
		if g.colors[u] == nocolor {
			g.dfs(u, color)
			color++
		}
	}
}

func (g *graph) isLink(s, t int) bool {
	return g.colors[s] == g.colors[t]
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	// construct graph and friendly colors
	g := constructGraph(sc)
	g.assignColor()

	// judge link
	q := nextInt(sc)
	for i := 0; i < q; i++ {
		s := nextInt(sc)
		t := nextInt(sc)

		if g.isLink(s, t) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

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

bool search(vector<int> member,int x){
  for(int i=0; i<member.size(); i++){
    if(member[i] == x)
      return true;
  }
    return false;
}
vector<int> update(vector<int> mother,vector<int> children,int join[],int a,int b){
  mother.push_back(b);
  join[b] = join[a];
  for(int i=0; i<children.size(); i++){
    int num=children[i];
    mother.push_back(num);
    join[num] = join[a];
  }

  return mother;
}
int main(){
  int n,m,join[10000],s,t;
  vector<int> group[10000];
  cin >> n >> m;

  for(int i=0; i<n; i++)
    join[i] = i;
    
  for(int i=0; i<m; i++){
    cin >> s >> t;
    bool flag = search(group[join[t]],s);

    if(!flag){
      int x = join[t];
      int y = join[s];

      if(x!=t || !group[x].empty())
	group[x] = update(group[x],group[y],join,x,y);


      else{
	group[y].push_back(t);
	join[x] = y;
      }
    }

  }
 
  int q;
  cin >> q;
  
  bool answer[10000];
  for(int i=0; i<q; i++){
    cin >> s >> t;
    
    if(join[s] == join[t])
      answer[i]=true;
    else
      answer[i]=false;
  }

  for(int i=0; i<q; i++){
    if(answer[i])
      cout << "yes\n";
    else
      cout << "no\n";
  }
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#define N 100000

using namespace std;
vector<int> v[N];
int group[N]={};
int g=0;

bool search(int s,int t){
  if(group[s]==group[t]&&group[s]>0) return true;
  group[s]=++g;
  queue<int> q;
  q.push(s);
  while(!q.empty()){
    int a=q.front();
    for(auto i=v[a].begin();i!=v[a].end();i++){
      if(group[*i]==0){
        group[*i]=g;
        q.push(*i);
      }
    }
    q.pop();
  }
  if(group[s]==group[t]&&group[s]>0){ 
    return true;
  }else{
    return false;
  }
}

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

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

}

C++: #include <cassert>
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <algorithm>
#include <bitset>
#include <complex>

#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#define rep(i,n) for(int i=0;i<(n); i++)
#define rep2(i,n) for(int i=1;i<=(n);i++)
#define WHITE 0
#define GRAY 1
#define BLACK 2

using namespace std;
typedef long long ll;
const int NMAX = 100000;
const int k = 200000;
static const int INF = 1<<21;
static const int NIL = -1;

int dp[3001][3001];
ll gcd(ll a, ll b){
if(a<b) swap(a,b);
    if(b==0) return a;
    return gcd(b, a%b);
}

int n,color[NMAX];
vector<int> G[NMAX];

void dfs(int r,int c){
    stack<int> S;
    S.push(r);
    color[r] = c;
    while(!S.empty()){
        int u=S.top();
        S.pop();
        rep(i,G[u].size()){
            int v=G[u][i];
            if(color[v]==NIL){
                color[v]=c;
                S.push(v);
            }
        }
    }
}

void assignColor(){
    int id=1;
    rep(i,n) color[i]=NIL;
    rep(u,n){
        if(color[u]==NIL){
            dfs(u,id++);
        }
    }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0); //この2行はより速度を向上させる
    // 追加２, 以降 cin の入力元が 'input.txt' になる


    int m,s,t,q;
    cin >> n >> m;
    rep(i,m){
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s); //無向グラフなので双方に格納する
    }
    assignColor(); //色塗り

    cin >> q;

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

C++: #include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

// union - find tree !!!!!!!!!!!!!!!!!!!!!!!!!
vector<int> par; //oya
vector<int> rnk; //ki no hu ka sa
// n????´???§?????????
void init(int n){
    par.resize(n);rnk.resize(n);
    FOR(i, 0, n){par[i] = i;rnk[i] = 0;}
}
//??¨??????????±???????
int find(int x){
    if(par[x] == x) return x;
    else return par[x] = find(par[x]);
}
//x??¨y????±??????????????????????
void Merge(int x, int y){
    x = find(x);y = find(y);
    if(x == y) return;
    if(rnk[x] < rnk[y])par[x] = y;
    else{par[y] = x;if(rnk[x] == rnk[y]) rnk[x]++;}
    return;
}

int main(){
  int n, m; cin >> n >> m;
  init(n);
  FOR(i,0,m){
    int a, b;
    cin >> a >> b;
    Merge(a, b);
  }
  int q;
  cin >> q;
  FOR(i,0,q){
    int a, b;
    cin >> a >> b;
    if(find(a) == find(b)){
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }
  return 0;
}