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>

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n, m;
struct node {
    int id;
    node* parent;
    int rank;
};

node find(node x){
    if(x.parent == NULL)
        return x;
    else
        x = find(*x.parent);
    return x;
}

void marge(node x, node y){
    int height_x = x.rank;
    int height_y = y.rank;
    x = find(x);
    y = find(y);
    if(x.id == y.id)
        return;
    if(height_x > height_y)
        y.parent = &x;
    else
        x.parent = &y;
    return;
}

bool judge(node x, node y){
    x = find(x);
    y = find(y);
    return x.id == y.id;
}

int main() {
    cin >> n >> m;
    node person[n];
    REP(i, n){
        person[i].id = i;
        person[i].parent = NULL;
        person[i].rank = 0;
    }
    REP(i, m){
        int s, t;
        cin >> s >> t;
        if(person[t].rank == 0){
            person[t].parent = &person[s];
            person[t].rank = person[s].rank + 1;
        } else if(person[s].rank == 0){
            person[s].parent = &person[t];
            person[s].rank = person[t].rank + 1;
        } else marge(person[s], person[t]);
    }
    int q;
    cin >> q;
    REP(i, q){
        int s, t;
        cin >> s >> t;
        if(judge(person[s], person[t]))
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <queue>
using namespace std;

#define NODE_NUM 100000

queue<int> que;

class Node
{
private:
	int next_num;
	int *next_node_list;
public:
	Node(){};
	void Init(int n);
	void AddNextNode(int id);
	bool Search(int st, int ed);
	bool *check;
	bool *link;
};

void Node::Init(int n)
{
	next_num = 0;
	next_node_list = new int[n];
	check = new bool[n];
	for (int i = 0; i < n; i++) {
		check[i] = false;
	}
	link = new bool[n];
	for (int i = 0; i < n; i++) {
		link[i] = false;
	}
}

void Node::AddNextNode(int id)
{
	next_node_list[next_num] = id;
	next_num++;
}

Node *Node_list;

bool Node::Search(int st, int ed)
{
	if (link[ed]) return true;

	for (int k = 0; k < next_num; k++) {
		Node_list[st].link[next_node_list[k]] = true;
		Node_list[next_node_list[k]].link[st] = true;
	}

	for (int i = 0; i < next_num; i++) {
		if (next_node_list[i] == ed) return true;
	}
	
	for (int j = 0; j < next_num; j++) {
		if (Node_list[next_node_list[j]].check[ed] == 0) {
			Node_list[next_node_list[j]].check[ed] = 1;
			que.push(next_node_list[j]);
		}
	}
	
	return false;
}

int main(void)
{
	//input
	int n;
	cin >> n;
	Node_list = new Node[n];
	for (int i = 0; i < n; i++) {
		Node_list[i].Init(n);
	}
	int m;
	cin >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		Node_list[s].AddNextNode(t);
		Node_list[t].AddNextNode(s);
	}
	
	//output
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		Node_list[s].check[t] = true;
		bool ret = Node_list[s].Search(s, t);
		while (!ret && !que.empty()) {
			ret = Node_list[que.front()].Search(s, t);
			que.pop();
		};
		while (!que.empty()) {
			que.pop();
		}
		for (int j = 0; j < n; j++) {
			Node_list[j].check[t] = false;
		}

		if (ret) {
			cout << "yes" << "\n";
		}
		else {
			cout << "no" << "\n";
		}
	}
	
	return 0;
}

C++: #include<stdio.h>
#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() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
        g[t].push_back(s);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        printf((color[s]==color[t]?"yes\n":"no\n"));
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG true
// sort(a.begin(), a.end(), std::greater<int>());

/*
std::vector<std::string> split(const std::string &input, char delimiter)
{
    std::istringstream stream(input);

    std::string field;
    std::vector<std::string> result;
    while (std::getline(stream, field, delimiter))
    {
        result.push_back(field);
    }
    return result;
}
*/
/*
int dfs(int foo, int timer)
{
    //foo is node number
    if (finds[foo].first != -1)
        return timer;
    finds[foo].first = ++timer;
    int result = timer;
    if (data[foo].size() != 0)
    {
        rep(i, data[foo].size())
        {
            result = dfs(data[foo][i], result);
        }
    }
    finds[foo].second = ++result;
    return result;
}
*/

int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> data[100000];
    int group[100000] = {0}, id = 1;
    rep(i, m)
    {
        int l, r;
        cin >> l >> r;
        data[l].push_back(r);
        data[r].push_back(l);
    }
    queue<int> que;
    rep(i, n)
    {
        que.push(i);
        if (group[i] == 0)
            group[i] = id;
        while (!que.empty())
        {
            int foo = que.front();
            que.pop();
            rep(i, data[foo].size())
            {
                if (group[data[foo][i]] == 0)
                {
                    group[data[foo][i]] = id;
                    que.push(data[foo][i]);
                }
            }
        }
        id++;
    }
    int q;
    cin >> q;
    rep(i, q)
    {
        int a, b;
        cin >> a >> b;
        if (group[a] == group[b])
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
    return 0;
}