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 MAXN = 100005;
const int NIL = -1;

int n;
vector<int>G[MAXN];
int color[MAXN];

void dfs(int s, int c)
{
	stack<int> S;
	S.push(s);
	color[s] = 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 AssighColor()
{
	int id = 1;
	for(int i = 0; i < n; i++)
		color[i] = NIL;
	for(int i = 0; i < n; i++)
	{
		if(color[i] == NIL)
			dfs(i, 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);
	}
	
	AssighColor();
	
	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 <bits/stdc++.h>
using namespace std;

struct UnionFind{
  int n;
  vector<int> r, p;
  UnionFind() {}
  UnionFind(int sz): n(sz), r(sz, 1), p(sz, 0){ iota(p.begin(), p.end(), 0); }
  int find(int x) {
    return (x == p[x] ? x : p[x] = find(p[x]));
  }
  bool same(int x, int y) {
    return find(x) == find(y);
  }
  void unite(int x, int y){
    x = find(x); y = find(y);
    if ( x == y ) return;
    if ( r[x] < r[y] ) swap(x, y);
    r[x] += r[y];
    p[y] = x;
  }
};

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

  UnionFind uf(n);
  for ( int i = 0; i < m; i++ ) {
    int s, t;
    cin >> s >> t;
    uf.unite(s, t);
  }

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

C++: #include <iostream>
#include <vector>
#include <stack>

int main() {
	// 入力
	int n, m;
	std::cin >> n >> m;
	std::vector<std::vector<int>> vec(n);
	std::vector<int> d(n, -1);
	std::stack<int>  s;

	for (int i = 0; i < m; i++) {
		int a, b;
		std::cin >> a >> b;
		vec[a].push_back(b);
		vec[b].push_back(a);
	}

	// 連結成分分解
	for (int i = 0; i < n; i++) {
		if (d[i] != -1) continue;
		if (vec[i].size() == 0) continue;
		s.push(i);
		while(!s.empty()){
			int x = s.top();
			s.pop();
			for (int j = 0; j < vec[x].size(); j++) {
				if (d[vec[x][j]] == -1) {
					d[vec[x][j]] = i;
					s.push(vec[x][j]);
				}
			}
		}
	}

	int q;
	std::cin >> q;
	while (q--) {
		int a, b;
		std::cin >> a >> b;
		if (d[a] != -1 && d[b] != -1 && d[a] == d[b]) {
			std::cout << "yes" << std::endl;
		}
		else {
			std::cout << "no" << std::endl;
		}
	}
}

C++: #include <iostream>
#include<string>
#include<cmath>
#include<algorithm>
#include<cctype>
#include<queue>
#include<stack>
#include<stdio.h>
#include<vector>
#include<set>
#include<map>
#include<array>
#include<iomanip>
#define rep(i,n) for(int i=0;i<n;i++)
typedef int long long ll;

using namespace std;

static const int MAX=1000000;
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;
    rep(i,n)color[i]=nil;
    rep(i,n){
        if(color[i]==nil)dfs(i,id++);
    }
    
    
}

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

return 0;
}

C++: //#define scanf_s scanf
#include <string>
#include <stdio.h>
#include <math.h>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

#define MAX 100
#define _MAX 1000
struct Graph
{
	int id, k = 0;
	list<int> node;
	int d = -1;
};
Graph G[MAX];
list<int> co;
int bo = false;
void Connect(Graph *g,Graph *f)
{
	if (g->k >= 0) {
		int a = true;
		co.push_back(g -> id);
		printf("%d,", g->id);
		for (auto i = g->node.begin(); i != g->node.end(); ++i) {
			if (&G[*i] == f) { bo = true; return; }
			for (auto j = co.begin(); j != co.end(); ++j) {
				if (*j == *i) {
					a = false;
					break;
				}
			}
			if(a) return Connect(&G[*i], f);
			a = true;
		}
	}
}
int main(void)
{
	int n, m, q, a, b;
	int qq[_MAX] = { 0 };
	scanf_s("%d %d", &n, &m);
	for (int i = 0; i < m; ++i) {
		scanf_s("%d %d", &a, &b);
		G[a].id = a; G[b].id = b;
		++G[a].k; G[a].node.push_back(b);
		++G[b].k; G[b].node.push_back(a);
	}
	scanf_s("%d", &q);
	for (int i = 0; i < q; ++i) {
		scanf_s("%d %d", &a, &b);
		bo = 0;
		Connect(&G[a], &G[b]);
		qq[i] = bo;
		co.clear();
	}
	for (int i = 0; i < q; ++i) {
		if(qq[i]) printf("yes\n");
		else printf("no\n");
	}
}

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[100000],s,t;
  vector<int> group[100000];
  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);
	group[y].clear();
      }

      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";
  }
}