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>
#include <stack>
using namespace std;

const int Max = 100000;
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){
                S.push(v);
                color[v] = c;
                // cout << color[v] << endl;
            }
        }
    }
}
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 m, u, v, q;
    cin >> n >> m;
    for(int i=0; i<m; i++){
        cin >> u >> v;
        G[u].push_back(v);
        G[v].push_back(u);
    }

    assignColor();
    
    cin >> q;
    for(int i=0; i<q; i++){
        cin >> u >> v;
        cout << color[u] << color[v] << endl;
        if(color[u] == color[v]) cout << "yes\n";
        else cout << "no\n";
    }

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
//#define ll long long
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
#define rep(i, n) REP(i, 0, n)
#define rep_rev(i, n) for (int (i) = (int)(n) - 1 ; (i) >= 0 ; --(i))
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
#define all(x) (x).begin(),(x).end()
ll t1,t2;
const ll mod = 1000000007;
const int INF = 1e9;
const ll INFLONG = 1e18;
void swap(ll *x,ll *y){
  ll tmp;
  tmp = *x;
  *x = *y;
  *y = tmp;
}
vector<ll> kinds(100000,-1);
vector<ll> vec[100000];
void dfs(ll k,ll num){
  if(kinds[k] != -1){
    return;
  }
  kinds[k] = num;
  for(auto itr:vec[k]){
    dfs(itr,num);
  }
}
int main(){
  ll n,m;
  cin >> n >> m;
  rep(i,m){
    cin >> t1 >> t2;
    vec[t1].push_back(t2);
    vec[t2].push_back(t1);
  }
  rep(i,n){
    dfs(i,i);
  }
  ll q;
  cin >> q;
  rep(i,q){
    cin >> t1 >> t2;
    if(kinds[t1] == kinds[t2]){
      cout << "yes" << endl;
    }else{
      cout << "no" << endl;
    }
  }
  return 0;
}

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

vector<int> list[100000];
int num[100000];
int n,m;

void bfs(int s,int sign){

  queue<int> Q;
  Q.push(s);

  while(!Q.empty()){
    int k=Q.front(); Q.pop();
    for(int i=0;i<list[k].size();i++){
      int temp=list[k][i];
      if(num[temp]==-1){ //未訪問なら
        Q.push(temp); num[temp]=sign;
      }
    }
  }
}
int main(){

  cin>>n>>m;

  for(int i=0;i<m;i++){
    int u,v; cin>>u>>v;
    list[u].push_back(v);
    list[v].push_back(u);
  }
  fill(num,num+100000,-1);
  int q; cin>>q;

  int sign=0;
  for(int i=0;i<n;i++){
    if(num[i]==-1){
      bfs(i,sign++);
    }
  }
  for(int i=0;i<q;i++){
    int s,t; cin>>s>>t;
    if(num[s]==num[t] && (num[s]!=-1 || num[t]!=-1)){
      cout<<"yes\n";
    }else{
      cout<<"no\n";
    }
  }

}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int N = 100000;
static const int NIL = -1;
int n;
vector<int> G[N];
int reach[N];
void dfs(int r, int c) {
    stack<int> S;
    S.push(r);
    reach[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 (reach[v] == NIL) {
                reach[v] = c;
                S.push(v);
            }
        }
    }
}
void assign() {
    int id = 1;
    for (int i = 0; i < n; i++) reach[i] = NIL;
    for (int u = 0; u < n; u++)
        if (reach[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);
    }
    assign();
    cin >> q;
    for (int i = 0; i < q; i++) {
        cin >> s >> t;
        if (reach[s] == reach[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

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

void boo(int b[], int y[], int w, int m){
	for(int i = 0; i < m; i++){
		if(b[i] == w) {
			if(y[b[i + m]] != -1)
				y[b[i + m]] = 1;
		}
	}
	for(int i = m; i < m * 2; i++){
		if(b[i] == w) {
			if(y[b[i - m]] != -1)
				y[b[i - m]] = 1;
		}
	}
}

int foo(int a, int s, int b[], int m, int n){
	int z = 0, y[100100] = {}, k = 1;
	y[a] = 1;
	while(k){
		k = 0;
		for(int i = 0; i < n; i++){
			if(y[i] == -1) continue;
			else if(y[i] == 1){ 
				if(i == s){
					z = 1;
					k = 0;
					break;
				} else{
					k = 1;
					y[i] = -1;
					boo(b, y, i, m);
				}
			}
		}
	}
	return z;
	
}

int main(){
	int b[200100];
	int n, m, q, a, s;
	int i, j, k;
	cin>>n>>m;
	for(i = 0; i < m; i++){
		cin>>b[i]>>b[m + i];
	}

	cin>>q;

	for(i = 0; i < q; i++){
		cin>>a>>s;
		if(foo(a, s, b, m, n) == 1){
			cout<<"yes"<<endl;
		} else {
			cout<<"no"<<endl;
		}
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>
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 topId, int c) {
    stack<int> S;
    S.push(topId);
    color[topId] = 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;
}