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++: // 連結成分
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define NIL -1

vector<int> G[100005];
int color[100005];
int n,col;

void dfs(int r, int c);
void assign_number();

int main(){
    int m;
    cin >> n >> m;
    for(int i = 0; i < m; i++){
        int s,t; cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    col = 0;
    assign_number();
    
    int q;
    cin >> q;
    
    for(int i = 0; i < q; i++){
        int s,t; cin >> s >> t;
        cout << (color[s] == color[t] ? "yes" : "no") << endl;
    }
    return 0;
}

void assign_number(){
    // 未訪問の頂点を選んで探索していく
    for(int i = 0; i < n; i++){
        color[i] = NIL;
    }

    for(int i = 0; i < n; i++){
        if(color[i] == NIL){
            dfs(i,col); col++;
        }
    }
}

void dfs(int r, int c){
    // 頂点rから探索しそのグループにcの番号をふる
    stack<int> s;
    s.push(r);
    color[r] = c;

    while(!s.empty()){
        int top = s.top();
        s.pop();
        int size = G[top].size();
        for(int i = 0; i < size; i++){
            int v = G[top][i];
            if(color[v] == NIL){
                // まだ探索されていない頂点
                color[v] = c;
                s.push(v);
            }
        }
    }

}

C++: #include <cstdio>
#include <vector>
using namespace std;
const int MAXN = 1e5 + 7;
int col = 1;
int idx[MAXN];
vector<int> G[MAXN];
void dfs(int cur) {
	idx[cur] = col;
	for (int i = 0; i < G[cur].size(); i++) {
		if (!idx[G[cur][i]]) dfs(G[cur][i]);
	}
}
int main() {
    int n, m;
    scanf("%d%d", &n, &m);
    while (m--) {
    	int s, t;
    	scanf("%d%d", &s, &t);
    	G[s].push_back(t);
    	G[t].push_back(s);
	}
	for (int i = 0; i < n; i++) {
		if (!idx[i]) {
			dfs(i);
			col++;
		}
	}
	int q;
	scanf("%d", &q);
	for (int i = 0; i < q; i++) {
		int s, t;
		scanf("%d%d", &s, &t);
		if (idx[s] == idx[t]) printf("yes\n");
		else printf("no\n");
	}
	return 0;
}

C++: #include<stack>
#include<queue>
#include<conio.h>
#include<string>
#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
queue<int> Q;
vector<int> G[100000];
bool flag = false;
int s, t;
int color[100000];

void a(){
	while (!Q.empty()){
		Q.pop();
		for (int i = 0; i < G[s].size(); i++){
			//_getch();
			//cout << G[s][i] << endl;
			if (G[s][i] == t){
				flag = true;
				while (!Q.empty()) Q.pop();
				return;
			}
			else if (color[i] == 0){
				Q.push(G[s][i]);
				color[i] = 1;
			}
		}
		if (!Q.empty())s = Q.front();
	}
}

int main(){
	int n, 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);
	}
	cin >> q; fill(color, color + 100000, 0);
	for (int i = 0; i < q; i++){
		cin >> s >> t;
		Q.push(s);
		a();
		if (flag) cout << "yes" << endl;
		else cout << "no" << endl;
		flag = false;
		fill(color, color + 100000, 0);
	}

	return 0;
}

C++: /* ALDS1_11_D: Connected Components */

#include <iostream>
#include <vector>
#include <stack>
using std::vector;
using std::stack;

void grouping(int id, int group_id, int group_ids[], vector<int> sns[]) {
    stack<int> S;
    S.push(id);
    group_ids[id] = group_id;

    while(! S.empty()) {
        id = S.top();
        S.pop();
        vector<int> friends = sns[id];
        for (int i = 0; i < friends.size(); i++) {
            int friend_id = friends[i];
            if (group_ids[friend_id] < 0) {
                group_ids[friend_id] = group_id;
                S.push(friend_id);
            }
        }
    }
}

void assign_groups(int n_users, vector<int> sns[], int group_ids[]) {
    int group_id = 0;
    std::fill_n(group_ids, n_users, -1);
    for (int id = 0; id < n_users; id++) {
        if (group_ids[id] < 0) {
            grouping(id, group_id, group_ids, sns);
            group_id++;
        }
    }
}

int main() {
    std::ios::sync_with_stdio(false);

    int n_users, n_relations;
    std::cin >> n_users >> n_relations;

    int id, friend_id, n_friends;
    vector<int> *sns = new vector<int>[n_users];
    for (int i = 0; i < n_relations; i++) {
        std::cin >> id >> friend_id;
        sns[id].push_back(friend_id);
        sns[friend_id].push_back(id);
    }

    int group_ids[n_users];
    assign_groups(n_users, sns, group_ids);

    int n_questions;
    std::cin >> n_questions;

    for (int i = 0; i < n_questions; i++) {
        std::cin >> id >> friend_id;
        bool same_group = group_ids[id] == group_ids[friend_id];
        std::cout << ( same_group ? "yes" : "no" ) << "\n";
    }
    return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <vector>
using namespace std;

const int maxn = 100000 + 5;
int color[maxn];
bool vis[maxn];
vector <int> G[maxn];

void dfs(int u, int c)
{
    vis[u] = true;
    color[u] = c;

    for (int i = 0; i < G[u].size(); i++)
        if (!vis[G[u][i]])
        dfs(G[u][i], c);
}

int main()
{
    int n, m;
    while (scanf("%d %d", &n, &m) != EOF)
    {
        for (int i = 0; i < n; i++)
            G[i].clear();

        int u, v;
        for (int i = 0; i < m; i++)
        {
            scanf("%d %d", &u, &v);
            G[u].push_back(v);
            G[v].push_back(u);
        }

        memset(color, 0, sizeof(color));
        memset(vis, false, sizeof(vis));

        int c = 0;
        for (int i = 0; i < n; i++)
        {
            if (!vis[i])
            {
                ++c;
                dfs(i, c);
            }
        }

        int q;
        scanf("%d", &q);
        while (q--)
        {
            int u, v;
            scanf("%d %d", &u, &v);
            if (color[u] == color[v])
                printf("yes\n");
            else
                printf("no\n");
        }
    }
    return 0;
}