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 <stack>
using namespace std;

const int N = 100000;
const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
const int NIL = -1;

int n, M[N][N];
int color[N], cc[N], cp = 0;
int nt[N];

int next(int u){
	for (int v = nt[u]; v <= n; v++){
		nt[u] = v + 1;
		if (M[u][v]) return v;
	}
	return NIL;
}

void dfs_visit(int r){
	for (int i = 0; i < n; i++) nt[i] = 0;

	stack<int> S;
	S.push(r);
	color[r] = GRAY;
	cc[r] = cp;

	while (!S.empty()){
		int u = S.top();
		int v = next(u);
		if (v != NIL){
			if (color[v] == WHITE){
				color[v] = GRAY;
				cc[v] = cp;
				S.push(v);
			}
		}
		else {
			S.pop();
			color[u] = BLACK;
		}
	}
	cp++;
}

void dfs(){
	for (int i = 0; i < n; i++){
		color[i] = WHITE;
		nt[i] = 0;
	}

	for (int u = 0; u < n; u++){
		if (color[u] == WHITE) dfs_visit(u);
	}

}

int main(){
	int m, q;
	cin >> n >> m;
	for (int i = 0; i < n; i++){
		for (int j = 0; j < n; j++) M[i][j] = 0;
	}
	for (int i = 0; i < m; i++){
		int s, t;
		cin >> s >> t;
		M[s][t] = M[t][s] = 1;
	}

	dfs();

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

	return 0;
}

C++: #include<iostream>
#include<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<tuple>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;

typedef pair<int, int> P;

vector<vector<int>> a(100000);
vector<int> comp(100000, 0);

void dfs(int s, int id) {
	stack<int> st;
	st.push(s);
	comp[s] = id;
	while (!st.empty()) {
		int i = st.top();
		int k = a[i].size();
		REP(j, k + 1) {
			if (j < k) {
				int t = a[i][j];
				if (comp[t] != id) {
					comp[t] = id;
					st.push(t);
					break;
				}
			}
			else st.pop();
		}
	}
}

void divide(int size) {
	int s = 0;
	int id = 1;
	while (1) {
		dfs(s, id);
		while (s < size && comp[s]>0) s++;
		if (s == size) break;
		id++;
	}
	return;
}

int main() {
	//cin.tie(0);
	//ios::sync_with_stdio(false);

	int n, m;
	scanf("%d %d", &n, &m);
	//cin >> n >> m;
	REP(i, m) {
		int s, t;
		scanf("%d %d", &s, &t);
		//cin >> s >> t;
		a[s].push_back(t);
		a[t].push_back(s);
	}
	int q;
	cin >> q;
	divide(n);
	REP(i, q) {
		int s, t;
		scanf("%d %d", &s, &t);
		//cin >> s >> t;
		if (comp[s] == comp[t]) printf("yes\n");
		else printf("no\n");
	}

	return 0;
}

C++: #include<bits/stdc++.h>
#define same(a,b) (find(a)==find(b))
#define uni(a,b) fa[find(a)]=find(b)
#define init(n) for(int i=0;i<n;i++) fa[i]=i

int fa[100100];

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

int main()
{
	int n,m;
	scanf("%d%d",&n,&m);
	init(n);
	for(int i=0;i<m;i++)
	{
		int u,v;
		scanf("%d%d",&u,&v);
		uni(u,v);
	}
	int q;
	scanf("%d",&q);
	for(int i=0;i<q;i++)
	{
		int u,v;
		scanf("%d%d",&u,&v);
		if(same(u,v)) printf("yes\n");
		else printf("no\n");
	}
	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(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) des(u,id++);
  }
 }
int main (){
  int s,t,q,m;

  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 <stdio.h>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <math.h>
#include <queue>
#include <string.h>
#include <stdlib.h>
#include <map>
#include <set>
using namespace std;
typedef unsigned long long ull;
typedef  long long ll;
class UnionFind {
public:
	vector<int> Parent;
	UnionFind(int N) {
		Parent = vector<int>(N, -1);
	}
	int root(int A) {
		if (Parent[A] < 0) {
			return A;
		}
		return Parent[A] = root(Parent[A]);
	}

	int size(int A) {
		return -Parent[root(A)];
	}

	bool connect(int A, int B) {
		A = root(A);
		B = root(B);
		if (A == B) {
			return false;
		}
		if (size(A) < size(B)) {
			swap(A, B);
		}

		Parent[A] += Parent[B];
		Parent[B] = A;

		return true;
	}

};
int main()
{
	int n, m, q;
	cin >> n >> m;
	UnionFind uni(n);
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		uni.connect(s, t);
	}
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (uni.root(s) == uni.root(t)) {
			cout << "yes" << endl;
		}
		else {
			cout << "no" << endl;
		}
	}

	return 0;
}