Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

C++: using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _20180319_AOJ
{
    class ALDS1_11D
    {
        static void Main(string[] args)
        {
            for (;;)
            {
                string line = Console.ReadLine();
                if (string.IsNullOrEmpty(line))
                {
                    break;
                }

                int[] n_m = line.Split(' ').Select(int.Parse).ToArray();
                int n = n_m[0];
                int m = n_m[1];
                int[,] matrix = new int[n, n];

                for (int i = 0; i < m; i++)
                {
                    int[] s_t = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
                    matrix[s_t[0], s_t[1]] = 1;
                    matrix[s_t[1], s_t[0]] = 1;
                }

                int[] group = new int[n];
                int gn = 0;
                for (int i = 0; i < n; i++)
                {
                    if (group[i] == 0)
                    {
                        gn++;
                        group[i] = gn;
                    }

                    gn = group[i];
                    for (int t = 0; t < n; t++)
                    {
                        if (matrix[i, t] == 1)
                        {
                            int tn = group[t];
                            if (tn > 0)
                            {
                                Replace(group, tn, gn);
                            }
                            else
                            {
                                group[t] = gn;
                            }
                        }
                    }
                }

                int q = int.Parse(Console.ReadLine());
                for (int i = 0; i < q; i++)
                {
                    int[] s_t = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
                    if (group[s_t[0]] == group[s_t[1]])
                    {
                        Console.WriteLine("yes");
                    }
                    else
                    {
                        Console.WriteLine("no");
                    }
                }
            }
        }

        static void Replace<T>(T[] arr, T source, T dest)
        {
            for (int i = 0; i < arr.Length; i++)
            {
                if (arr[i].Equals(source))
                {
                    arr[i] = dest;
                }
            }
        }
    }
}

C++: /* ALDS1_11_D: Connected Components */

#include <iostream>
#include <vector>
using std::vector;

bool is_connectable(vector<int> sns[], int id, int goal_id) {
    vector<int> friends = sns[id];
    for (int i = 0; i < friends.size(); i++) {
        int friend_id = friends[i];
        if (friend_id == goal_id || is_connectable(sns, friend_id, goal_id))
            return true;
    }
    return false;
}

int main() {
    std::ios::sync_with_stdio(false);

    int n_users, n_relations;
    std::cin >> n_users >> n_relations;

    int id, friend_id, n_friends;
    vector<int> *sns = new vector<int>[n_users];
    for (int i = 0; i < n_relations; i++) {
        std::cin >> id >> friend_id;
        sns[id].push_back(friend_id);
    }

    int n_questions;
    std::cin >> n_questions;

    for (int i = 0; i < n_questions; i++) {
        std::cin >> id >> friend_id;
        bool connectable = is_connectable(sns, id, friend_id);
        std::cout << ( connectable ? "yes" : "no" ) << "\n";
    }
    return 0;
}

C++: #include <iostream>
#include <stack>
#include <vector>
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++: #include <cstdio>
#include <algorithm>
#define rep(i, n) for(int i=0; i<(n); ++i)

int parent[100005];

int find(int x){
   if( parent[x] == x )return x;
   return parent[x] = find( parent[x] );
}

void unite(int x, int y)
{
   x = find(x);
   y = find(y);

   if(x == y)return;
   parent[x] = y;
}

int main()
{
   int N, M;
   int x, y, tmp;
   scanf("%d%d", &N, &M);
   std::iota(parent, parent + N, 0);

   rep(i, M){
      scanf("%d%d", &x, &y);
      unite(x, y);
   }

   int Q;
   scanf("%d", &Q);
   while(Q--){
      scanf("%d%d", &x, &y);
      puts( find(x) == find(y) ? "yes" : "no" );
   }
}

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

const int maxm = 100000 + 5;
const int maxn = 100000 + 5;

struct Edge{
	int to,next;
}G[maxm<<1];

int head[maxn],cnt = 0;
int color[maxn];
bool vis[maxn];

void Insert(int u,int v){
	G[++cnt].next = head[u];
	G[cnt].to = v;
	head[u] = cnt;
}

void Dfs(int u,int c){
	vis[u] = true;
	color[u] = c;
	for(int e = head[u];e; e = G[e].next){
		int v = G[e].to;
		if(!vis[v]){
			Dfs(v,c);
		}
	}
}

int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i = 1;i <= m; i++){
		int u,v;
		scanf("%d%d",&u,&v);
		Insert(u,v);
		Insert(v,u);
	}
	for(int i = 1;i <= n; i++){
		if(!vis[i]){
			Dfs(i,i);	
		}
	}
	int q;
	scanf("%d",&q);
	for(int i = 1;i <= q; i++){
		int u,v;
		scanf("%d%d",&u,&v);
		if(color[u] == color[v])printf("yes\n");
		else printf("no\n");
	}
}

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();

  sin>>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;
}