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;
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;

  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 <stack>
#include <iostream>
using namespace std;
int G[10000][10000];
int vis[100000];
int n;

bool dfs(int s, int t)
{
    if (G[s][t] == 1 || G[t][s] == 1) return true;
    vis[s] = 1;
    for (int i = 0; i < n; i++)
    {
        if (G[s][i] == 1 && vis[i] == 0)
            {
                bool a = (dfs(i,t)); 
                if(a) 
                {
                    vis[s] = 0;
                    return a;
                }
            }

    } 
    vis[s] = 0;
    return false;
}

int main()
{
    //freopen("in3.txt","r",stdin);
    int m;
    scanf("%d %d",&n, &m);
    for (int i = 0; i < n; i++)
    {
        vis[i] = 0; 
    } 
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            G[i][j] = 0; 
        }  
    } 
    for (int i = 0; i < m; i++)
    {
        int s, t;
        scanf("%d %d",&s,&t); 
        G[s][t] = 1;
        G[t][s] = 1;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)||dfs(t,s)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include<stdio.h>
#include<queue>

using namespace std;

const int MAX = 100000;

int parent(int table[], int child) {

	while (table[child] != -1) {
		q.push(child);
		child = table[child];
	}
	return child;
}

int main() {
	int n, m, q;
	int table[MAX];

	scanf("%d %d", &n, &m);

	for (int i = 0; i < n; i++)table[i] = -1;
	for (int i = 0; i < m; i++) {
		int s, t;
		scanf("%d %d", &s, &t);
		
		int ps = parent(table, s);
		int pt = parent(table, t);
		if (ps != pt) {
			table[ps] = pt;
		}
	}

	scanf("%d", &q);

	for (int i = 0; i < q; i++) {
		int s, t;
		
		scanf("%d %d", &s, &t);

		int ps = parent(table, s);
		int pt = parent(table, t);

		if (ps == pt) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	return 0;
}

C++: //By Vlgd
//By Vlgd
#include<bits/stdc++.h>
using namespace std;
const int N=100000;
int n,m,d[N],t=0;
vector<int>G[N];
stack<int>S;
void dfs(int r,int cnt){
	S.push(r);
	d[r]=cnt;
	while(!S.empty()){
		int u=S.top();S.pop();
		for (int i=0;i<G[u].size();i++){
			int v=G[u][i];
			if (d[v]==-1){
				d[v]=cnt;
				S.push(v);
			}
		}
	}
}
int main(){
	scanf("%d%d",&n,&m);
	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(d,-1,sizeof(d));
	for (int i=0;i<n;i++) if (d[i]==-1) dfs(i,t++);
	int q;
	scanf("%d",&q);
	for (int i=0;i<q;i++){
		scanf("%d%d",&u,&v);
		if (d[u]==d[v]) printf("yes\n");
		else printf("no\n");
	} 
}

C++: // ALDS1_11_D.cpp
// Graph I - Connected Components

#include <iostream>
#include <vector>
using namespace std;

bool isFriend(vector<vector<int>> &sns, vector<int> &arrived, int x, int y)
{
    if (sns[x][y] == 1) return true;
    bool res = false;
    arrived[x] = 1;
    for (int i = 0; i < sns.size(); i++) {
        if (sns[x][i] == 1 && !arrived[i]) {
            bool tmp = isFriend(sns, arrived, i, y);
            if (tmp) {
                res = true;
                break;
            }
        }
    }
    return res;
}

int main()
{
    int m, n, q;
    cin >> n >> m;
    vector<vector<int> > sns(n, vector<int>(n, 0));
    int x, y;
    for (int i = 0; i < m; i++) {
        cin >> x >> y;
        sns[x][y] = 1;
        sns[y][x] = 1;
    }

    cin >> q;
    while (q--) {
        vector<int> arrived(n);
        cin >> x >> y;
        bool res = isFriend(sns, arrived, x, y);
        if (res) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

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

int main() {
	int n,m,q,k;
	int s,t;
	int i,j;
	queue<int> nq;
	vector<vector<int> > node;
	vector<int> ngrp;

	scanf("%d%d",&n,&m);
	node.resize(n);
	ngrp.resize(n);

	for(i=0;i<m;++i) {
		scanf("%d%d",&s,&t);
		node[s].push_back(t);
		node[t].push_back(s);
	}

	for(i=0;i<n;++i) {
		ngrp[i]=-1;
	}

	for(i=0; i<n; ++i) {
		if(ngrp[i]==-1) {
			nq.push(i);
			ngrp[i]=i;
			while(!nq.empty()) {
				k=nq.front();
				for(j=0;j<(int)node[k].size();++j) {
					if(ngrp[node[k][j]]==-1) {
						ngrp[node[k][j]]=i;
						nq.push(node[k][j]);
					}
				}
				nq.pop();
			}
		}
	}
	scanf("%d",&q);
	for(i=0;i<q;++i) {
		scanf("%d%d",&s,&t);
		printf((ngrp[s]==ngrp[t])?"yes\n":"no\n");
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
const int MAX=100000,NIL=-1;
int n,color[MAX];
vector<int> G[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 assign(){
    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(void){
    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);
    }
    assign();
    cin >> q;
    for(int i=0;i<q;i++){
        cin >> s >> t;
        if(color[s]==color[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
}