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++: #define _CRT_SECURE_NO_WARNINGS

#include<iostream>
#include<functional>
#include<algorithm>
#include<stack>
#include<queue>
#include<iomanip>
#include<set>
#include<map>
#include<utility>
#include<string>
#include<vector>

using namespace std;

#define LL long long
const int dx[4] = { 1,-1,0,0 };
const int dy[4] = { 0,0,1,-1 };
bool OOA(int x,int y,int H,int W){return (0<=x&&x<H)&&(0<=y&&y<W);}

struct Graph {
	int V, E, t;
	//vector<int>cost;
	vector<int>gr;
	//vector<bool>vzt;
	vector<vector<int>>adj;
	void init(int dflt) {//dflt!=0
		adj = vector<vector<int>>(V + 1);
	//	cost = vector<int>(V + 1, dflt);
		gr = vector<int>(V + 1, dflt);
	//	vzt = vector<bool>(V + 1, false);
	}

	void dfs(int now) {
		if (gr[now] == -1) { gr[now] = t; }
		else return;
		for (int i = 0;i<adj[now].size();i++)dfs(adj[now][i]);
		return;
	}

	void CC(){
		for(int i=0;i<V;i++){
			if(gr[i]==-1){
				t=i;
				dfs(i);
			}
		}
		return;
	}
};

Graph G;
int n,m,q;

int main() {
	cin>>n>>m;
	G.V=n;
	G.init(-1);
	for(int i=0;i<m;i++){
		int s,t;
		cin>>s>>t;
		G.adj[s].push_back(t);
		G.adj[t].push_back(s);
	}
	G.CC();
	cin>>q;
	for(int i=0;i<q;i++){
		int s,t;
		cin>>s>>t;
		cout<<(G.gr[s]==G.gr[t]?"yes":"no")<<endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;

vector<vector<int>> GetAdjacencyList(int n, int m)
{
	vector<vector<int>> al(n);
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		al[s].push_back(t);
		al[t].push_back(s);
	}
	return al;
}

void BFS(int i, const vector<vector<int>>& al, vector<int>& group)
{
	queue<int> q;
	q.push(i);
	group[i] = i + 1;
	while (!q.empty()) {
		int node = q.front(); q.pop();
		for (const auto& item : al[node]) {
			if (group[item]) continue;
			q.push(item);
			group[item] = i + 1;
		}
	}
}

int main()
{
	int n, m;
	cin >> n >> m;
	vector<vector<int>> al = GetAdjacencyList(n, m);
	vector<int> group(n);
	for (int i = 0; i < n; i++) {
		if (!group[i]) BFS(i, al, group);
	}
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (group[s] == group[t]) cout << "yes" << endl;
		else cout << "no" << endl;
	}
}

C++: #include<iostream>    // ???????????????????§?????????£????????????
using namespace std;
#include<stdio.h>

typedef struct fox { int val; fox *prev, *next; } fox_t;

fox_t* init()
{
	fox_t* head = new fox_t;
	head->val = -1;
	head->next = NULL;
	head->prev = NULL;
	return head;
}

fox_t* make_tail(fox_t* head)
{
	fox_t* tail = new fox_t;
	tail->val = -1;
	head->next = tail;
	tail->next = NULL;
	tail->prev = head;
	return tail;
}

bool isEmpty(fox_t* head, fox_t* tail)
{
	return (head->next == tail ? true : false);
}

fox_t* b_insert(fox_t* tail, int data)
{
	fox_t* fox = new fox_t;
	fox->val = data;
	fox->prev = tail->prev;
	fox->next = tail;
	tail->prev->next = fox;
	tail->prev = fox;
	return fox;
}
// docking.
void unionfox(fox_t* head1, fox_t* tail1, fox_t* head2, fox_t* tail2)
{
	if(isEmpty(head1, tail1) || isEmpty(head2, tail2)) return;
	fox_t* fox = tail1->prev;
	cout << tail1->prev << endl;
	cout << head2->next << endl;
	fox->next = head2->next;
	head2->next->prev = fox;
	tail2->prev->next = tail1;
	tail1->prev = tail2->prev;
	delete tail2;
	delete head2;
}

int main()
{
	int color[1001];
	int c_num = 0;
	fox_t* foxhead[100001];
	fox_t* foxtail[100001];
	int i, n, m, q;
	int a, b;
	cin >> n >> m;
	for(i = 0; i < n; i++){
		color[i] = -1;
		foxhead[i] = init();
		foxtail[i] = make_tail(foxhead[i]);
	}
	int c_a, c_b, val;

	for(i = 0; i < m; i++){
		cin >> a >> b;
		c_a = color[a];
		c_b = color[b];
		if(c_a < c_b){ swap(c_a, c_b); swap(a, b); }  // color[a] >= color[b].
		if(c_a < 0 && c_b < 0){
			color[a] = c_num; color[b] = c_num;
			b_insert(foxtail[c_num], a);
			b_insert(foxtail[c_num], b);
			c_num++;
		}else if(c_b < 0){
			color[b] = c_a;
			b_insert(foxtail[c_a], b);
		}else if(c_a == c_b){
			continue;
		}else{ // color[a] != color[b].
			fox_t* fox = foxhead[c_b]->next;
			while(fox != foxtail[c_b]){
				val = fox->val;
				color[val] = c_a;
				fox = fox->next;
			};
			unionfox(foxhead[c_a], foxtail[c_a], foxhead[c_b], foxtail[c_b]);
		}
	}
	cin >> q;
	for(i = 0; i < q; i++){
		cin >> a >> b;
		if(color[a] >= 0 && (color[a] == color[b])){
			printf("yes\n"); }else{ printf("no\n"); 
			}
	}
	return 0;
}

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

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
int main() {
    cin>>n>>m;
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        cin>>s>>t;
        g[s].push_back(t);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    cin>>q;
    for(int i=0;i<q;i++){
        cin>>s>>t;
        cout<<(color[s]==color[t]?"yes\n":"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)dfs(u,id++);
    }
}

int main(){
    int s,t,m,q;

    cin >> n >> m; // n = ノードの数 m = 辺の数 

    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;
}