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;

bool DFS(const vector<vector<int> >& G, int a, int b) {
    if (G[a].size() == 0) return false;

    stack<pair<int, int> > S;
    vector<bool> is_visited(G.size(), false);

    int idx = 0;
    do {
        if (idx >= G[a].size()) {
            a   = S.top().first;
            idx = S.top().second;
            S.pop();
            idx++;
            continue;
        }
        if (G[a][idx] == b) return true;
        if (!is_visited[G[a][idx]]) {
            is_visited[G[a][idx]] = true;
            S.push(make_pair(a, idx));
            a   = G[a][idx];
            idx = 0;
            continue;
        }
        idx++;
    } while (!S.empty());
    return false;
}


int main(){
    int n, m;
    cin >> n >> m;

    vector<vector<int> > G(n);

    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

// for (int i = 0; i < n; i++) {
//     cout << i << " : ";
//     for (int j = 0; j < G[i].size(); j++){
//         cout << G[i][j] << " ";
//     }
//     cout << endl;
// }



    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        if (DFS(G, a, b)) {
            cout << "yes" << endl;
        } else {
            cout << "no"  << endl;
        }
    }
    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define ll long long
typedef complex<double> P;

int main() {
  int n, m; cin >> n >> m;
  vector<int> adj[n];

  for (int i = 0; i < m; i++) {
    int v, u; cin >> v >> u;
    adj[v].push_back(u);
    adj[u].push_back(v);
  }

  int q; cin >> q;
  int sd[n] = {};

  for (int i = 0; i < q; i++) {
    int s, t; cin >> s >> t;
    fill(sd, sd+n, 0);

    queue<int> que;
    que.push(s);
    bool f = false;

    while(!que.empty()) {
      int v = que.front(); que.pop();
      if(v == t) {
        f = true;
        break;
      }

      for (int j = 0; j < n; j++) {
        if(find(adj[v].begin(), adj[v].end(), j) != adj[v].end() && sd[j] == 0) {
          que.push(j);
        }
      }
    }

    cout << (f ? "yes" : "no") << endl;

  }
}

C++: #include <iostream>
#include <vector>
using namespace std;
#define MAX_V 100000

int n, v, q;
vector<int> G[MAX_V];
bool visited[MAX_V];
int group[MAX_V];


void init(){
  for(int i = 0; i < v; i++){
    visited[i] = false;
    group[i] = -1;
  }
}

void dfs(int v, int g){
  group[v] = g;
  visited[v] = true;
  for(int i = 0; i < G[v].size(); i++){
    int to = G[v][i];
    if(!visited[to]){
      dfs(to, g);
    }
  }
}

int main(void){
  cin >> v >> n;
  for(int i = 0; i < n; i++){
    int from, to;
    cin >> from >> to;
    G[from].push_back(to);
    G[to].push_back(from);
  }
  init();
  for(int i = 0; i < v; i++){
    if(!visited[i]) dfs(i, i);
  }
  cin >> q;
  for(int i = 0; i < q; i++){
    int s, t;
    cin >> s >> t;
    if(group[s] != -1 && group[t] != -1 && group[s] == group[t]) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  return 0;
}

C++: //Connected Component
#include <iostream>
#include <vector>

using namespace std;

static const int N = 100000;
int n, colors[N] = {};

void dfs(vector<vector<int>>  &G, int u, int c) {
    if(colors[u] != -1) return;
    colors[u] = c;
    for(auto v: G[u]) {
        dfs(G, v, c);
    }
}

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

    for(int i = 0; i < n; i++) colors[i] = -1;
    for(int i = 0; i < n; i++) {
        dfs(G, i, i);
    }

    cin >> q;
    for(int i = 0; i < q; i++) {
        cin >> s >> t;
        if(colors[s] == colors[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
}

C++: #include <iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAXN=100000;
static const int NIL=-1;
 vector<int>G[MAXN];
 int color[MAXN];
 int n;
 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 b,q;
    cin>>n>>b;
    int s,t;
    for(int i=0;i<b;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<vector>
#include<iostream>
using namespace std;

#define MAX_N 100000
int par[MAX_N];//親の要素
int rank_[MAX_N];

//n要素で初期化
void init(int n)
{
	for (int i = 0; i < n; i++)
	{
		par[i] = i;
		rank_[i] = 0;
	}
}

//木の根を求める
int root(int x)
{
	if (par[x] == x)
	{
		return x;
	}
	else
	{
		return par[x] = root(par[x]);
	}
}

//xとyが同じ集合に属するか　否か
bool same(int x, int y)
{
	return root(x) == root(y);
}

//xとyの属する集合を併合
void unite(int x, int y)
{
	x = root(x);
	y = root(y);
	if (x == y)
	{
		return;
	}

	if (rank_[x] < rank_[y])
	{
		par[x] = y;
	}
	else
	{
		par[y] = x;
		if (rank_[x] == rank_[y])
		{
			rank_[x]++;
		}
	}


}

int main()
{
	int n;
	cin >> n;//頂点の数
	int m;
	cin >> m;//辺の数

	//初期化
	init(n);

	//木を作る
	for (int i = 0; i < m; i++)
	{
		int a, b;
		cin >> a >> b;
		if (same(a, b))
		{
			continue;
		}
		else
		{
			unite(a, b);
		}
	}

	int q;//クエリの数
	cin >> q;

	for (int i = 0; i < q; i++)
	{
		int a, b;
		cin >> a >> b;
		if (same(a, b))
		{
			cout << "yes" << endl;
		}
		else if(!same(a, b))
		{
			cout << "no" << endl;
		}
	}

	return 0;





}