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<bits/stdc++.h>

using namespace std;

#define MAX 100000
const int NIL = -1;

int n;
vector<int> G[MAX];
int color[MAX];
void assignColor();
void bfs(int,int);

int main(){
  int s,t,m,q,i;
  cin >> n >> m;
  for(i = 0; i < m; i++){
    cin >> s >> t;
    G[s].push_back(t);
    G[t].push_back(s);
  }
  assignColor();
  cin >> q;
  for(i = 0; i < q; i++){
    cin >> s >> t;
    if( color[s] == color[t]){
      cout << "yes" << endl;
    }
    else{
      cout << "no" << endl;
    }
  }
  return 0;
}

void bfs(int r, int c){
  stack<int> S;
  S.push(r);
  int u,v,i;
  color[r] = c;
  while( !S.empty() ){
    u = S.top();
    S.pop();
    for(i = 0; i < G[u].size(); i++){
      v = G[u][i];
      if( color[v] == NIL){
        color[v] = c;
        S.push(v);
      }
    }
  }
}

void assignColor(){
  int id = 1;
  int i,u;
  for(i = 0; i < n; i++){
    color[i] = NIL;
  }
  for(u = 0; u < n; u++){
    if( color[u] == NIL){
      bfs(u,id++);
    }
  }
}

C++: //#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; ++i)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using namespace std;
using ll = int64_t;
using ld = long double;
using P = pair<int, int>;
using vs = vector<string>;
using vi = vector<int>;
using vvi = vector<vi>;
const int INF = 100010001;
const ll LINF = (ll)INF*INF*10;

struct UnionFind {
    vector<int> par; // 親を指すvector,-par[親]は木のサイズ
    UnionFind(int n):par(n, -1) {} // uniteで親を埋め込んでいく必要あり
    int root(int x) { // 親をたどる&データの整理
        if(par[x] < 0) return x;
        return par[x] = root(par[x]);
    }
    bool unite(int x, int y) { // データの結合
        x = root(x);
        y = root(y);
        if(x == y) return false;
        if(par[x] > par[y]) swap(x, y);
        par[x] += par[y];
        par[y] = x;
        return true;
    }
    bool same(int x, int y) {return root(x) == root(y);} // 所属判定
    int size(int x) {return -par[root(x)];} // 木のサイズ
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    UnionFind uft(n);
    rep(i, m) {
        int s, t;
        cin >> s >> t;
        uft.unite(s, t);
    }
    int q;
    cin >> q;
    while(q--) {
        int i, j;
        cin >> i >> j;
        cout << (uft.same(i, j)?"yes":"no") << endl;
    }
}

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;
}

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];
      group[join[s]].push_back(join[t]);
      
      for(int j=0; j<group[join[x]].size(); j++){
	group[join[s]].push_back(group[join[t]][j]);
	join[group[join[t]][j]]=join[s];
      }
	  
      join[x] = join[s];
    }
  }
 
  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<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++: #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(c);
    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;
}