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 <stdio.h>
#include <iostream>
#include <list>
using namespace std;

class Node
{
private:
public:
	Node();
	int id;
	list<int> next_node_list;
	int next_idx;
	void AddNextNode(int id);
	void SetGroup(int prev_id, int num);
	int group;
	void Init(int id);
};

Node::Node()
{
	group = 0;
	next_idx = 0;
}

void Node::AddNextNode(int id)
{
	next_node_list.push_back(id);
}

Node *Node_list;

void Node::SetGroup(int prev_id, int num)
{
	group = num;

	list<int>::iterator itr;
	itr = next_node_list.begin();
	for (int i = 0; i < next_idx; i++) {
		itr++;
	}
	
	for(; itr != next_node_list.end(); itr++){
		next_idx++;
		if (prev_id != *itr) {
			Node_list[*itr].SetGroup(id, num);
		}
	}
}

void Node::Init(int id)
{
	this->id = id;
}

int main(void)
{
	//input
	int n;
	cin >> n;
	Node_list = new Node[n]();
	for (int i = 0; i < n; i++) {
		Node_list[i].Init(i);
	}
	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);
	}

	//group
	int group = 1;
	for (int i = 0; i < m; i++) {
		if (Node_list[i].group) continue;
		Node_list[i].SetGroup(-1, group);
		group++;
	}
	
	//output
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		if (Node_list[s].group == Node_list[t].group && Node_list[s].group != 0) {
			cout << "yes" << "\n";
		}
		else {
			cout << "no" << "\n";
		}
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define Rep(i, n) for (int i = 0; i < (int)(n); i++)
#define BitRep(i, n) for (int i = 0; i < (int)(1 << n); i++)
#define Sum(vec) accumulate(vec.begin(), vec.end(), 0)
#define Sort(vec) sort(vec.begin(), vec.end())
#define Reverse(vec) reverse(vec.begin(), vec.end())
#define Next_permutation(vec) next_permutation(vec.begin(), vec.end())

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

class vertex{
public:
  vector<vertex*> to;
  bool visited;
  int num;
  int group;

  vertex(){
    visited=false;
  }
  
  void dfs(int group){
    visited=true;
    this->group = group;
    for(int i=0; i<to.size(); i++){
      if(!to[i]->visited) to[i]->dfs(group);
    }
  }
};

int main(){
  int n, m; cin >> n >> m;
  vertex graph[n];

  //隣接リストにグラフを格納
  int v, k, to;
  for(int i=0; i<m; i++){
    cin >> v >> to;
    graph[v].num = v;
    graph[v].to.push_back(&graph[to]);
  }

  //頂点0からdfsを行い、グループ分け(各連結成分ごとに1から昇順に番号をつける)
  for(int v=0, group=1; v<n; v++){
    if(!graph[v].visited){
      graph[v].dfs(group);
      group++;
    }
  }

  //回答を得る
  int q, v1, v2; cin >> q;
  bool ans[q];
  for(int i=0; i<q; i++){
    cin >> v1 >> v2;
    if(graph[v1].group==graph[v2].group) ans[i]=true;
    else ans[i]=false;
  }

  //回答出力
  for(int i=0; i<q; i++){
    if(ans[i]) cout << "yes" << endl;
    else cout << "no" << endl;
  }

  return 0;
}

C++: #include <stdio.h>
#include <stack>
using namespace std;
int G[100000][100000];
int vis[100000];
int n;

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

int main()
{
    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;
    } 
    int q,s,t;
    scanf("%d",&q);
    for (int i = 0; i < q; i++)
    {
        scanf("%d %d",&s,&t);
        if(dfs(s,t)) printf("yes\n");
        else printf("no\n");
    } 
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
#include <cstdio>
#define MAX 100005
#define NIL -1 
using namespace std;

int color[MAX];
int n,m,s,t,q;
vector<int> G[MAX];

void dfs(int x, int y) {
	stack<int> S;
	S.push(x);
	color[x]=y;
	while(!S.empty()) {
		int tmp=S.top();
		S.pop();
		for(int i=0;i<G[tmp].size();i++) {
			int l=G[tmp][i];
			if(color[l]==NIL) {
				color[l]=y;
				S.push(l);
			}
		}
	}
}

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

int main() {
	int i,j;
	scanf("%d %d",&n,&m);
	for(i=0;i<m;i++) {
		scanf("%d %d",&s,&t);
		G[s].push_back(t);
		G[t].push_back(s);
	}
	
	assigncolor();
	
	scanf("%d",&q);
	for(i=0;i<q;i++) {
		scanf("%d %d",&s,&t);
		if(color[s]==color[t]) printf("yes\n");
		else printf("no\n");
	}
	
	return 0;
}