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 <cstdio>
#include <vector>
#include <algorithm>
#include <map>
#include <numeric>
#include <string>
#include <cmath>
#include <iomanip>
#include <string>
#include <queue>
#include <list>
#include <stack>

using namespace std;

/* constant */

const int INF = 1 << 30;
const int mod = 1000000007;
const int MAX_N = 100000;

/* typedef */

typedef long long ll;

/* global variables */

vector< vector<int> > Adj(MAX_N, vector<int>());
vector<int> link(MAX_N, -1);
int n;

/* function */
void bfs(int start);

/* main */
int main() {

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

    for (int i = 0; i < n; i++) {
        if (link[i] == -1) {
            bfs(i);
        }
    }

    int q; cin >> q;
    for (int i = 0; i < q; i++) {
        int u, v; cin >> u >> v;
        if (link[u] == link[v]) {
            cout << "yes" << '\n';
        }
        else {
            cout << "no" << '\n';
        }
    }
}

void bfs(int start) {
    
    link[start] = start;
    queue<int> q;
    q.push(start);

    while (!q.empty()) {

        int cur = q.front(); q.pop();

        for (auto v : Adj[cur]) {

            if (link[v] == -1) {
                link[v] = start;
                q.push(v);
            }

        }

    }
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <stack>
#include <vector>
#include <algorithm>
#include <cmath>
#include <climits>
#include <cstring>
#include <queue>
#include <string>

using namespace std;

const double PI = 3.14159265358979;

vector<int> G[100000];
int visited[100000];

void dfs_stack(int node, int color) {

	stack<int> st;

	visited[node] = color;
	st.push(node);

	while (!st.empty()) {

		int u = st.top();
		bool isPop = true;
		for (int i = 0; i < G[u].size(); i++) {
			if (!visited[G[u][i]]) {
				visited[G[u][i]] = color;
				st.push(G[u][i]);
				isPop = false;
			}
		}
		if (isPop) {
			st.pop();
		}
	}
}

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

	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++)	{
		if (!visited[i])
			dfs_stack(i, i + 1);
	}

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

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <stdio.h>
#include <cmath>
#include <set>
#include <map>
using namespace std;

vector<vector<int> >g;
int n,m,q;

vector<bool>visited;
bool dfs(int s,int t){
    if(s==t)return true;
    visited[s]=true;
    for(int i=0;i<g[s].size();i++){
        if(!visited[g[s][i]]){
            if(dfs(g[s][i],t)){
                return true;
            }
        }
    }
    return false;
}
int main() {
    cin>>n>>m;
    g.resize(n);
    for(int i=0;i<m;i++){
        int s,t;
        cin>>s>>t;
        g[s].push_back(t);
        g[t].push_back(s);
    }
    cin>>q;
    for(int i=0;i<q;i++){
        visited.resize(n,false);
        int s,t;
        cin>>s>>t;
        cout<<(dfs(s,t)?"yes":"no")<<endl;
    }
    return 0;
}

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

bool search(vector<int> member,int x){
  for(int i=0; i<member.size(); i++){
    if(member[i] == x)
      return true;
  }
    return false;
}
vector<int> update(vector<int> mother,vector<int> children,int join[],int a,int b){
  mother.push_back(b);
  join[b] = join[a];
  for(int i=0; i<children.size(); i++){
    int num=children[i];
    mother.push_back(num);
    join[num] = join[a];
  }

  return mother;
}
int main(){
  int n,m,join[10000],s,t;
  vector<int> group[10000];
  cin >> n >> m;

  for(int i=0; i<n; i++)
    join[i] = i;
    
  for(int i=0; i<m; i++){
    cin >> s >> t;
    bool flag = search(group[join[t]],s);

    if(!flag){
      int x = join[t];

      if(x!=t || !group[x].empty())
	group[x] = update(group[x],group[s],join,x,s);


      else{
	group[s].push_back(t);
	join[x] = join[s];
      }
    }

  }
 
  int q;
  cin >> q;
  
  bool answer[10000];
  for(int i=0; i<q; i++){
    cin >> s >> t;
    
    if(join[s] == join[t])
      answer[i]=true;
    else
      answer[i]=false;
  }

  for(int i=0; i<q; i++){
    if(answer[i])
      cout << "yes\n";
    else
      cout << "no\n";
  }
}

C++: #include "bits/stdc++.h"

#define REP(i,num) for(int i=0;i<(num);++i)
#define ALL(c) c.begin(),c.end()
#define PRINTALL(c) for(auto& x:c){cout<<x<<' ';}cout<<endl;
#define PAIRCOMP(c,comp) [](const pair<ll,ll>& lhs,const pair<ll,ll>& rhs){return lhs.c comp rhs.c;}

using namespace std;
using ll = long long;

constexpr ll atcoder_mod = 1e9+7;

template<typename T=int>
T in(){T x; cin >> x; return (x);}
template<typename T=int,typename C=vector<T>>
C vecin(int N){C x(N);REP(i,N){x[i]=in<T>();}return move(x);}

void vout(){cout << endl;}
template<typename Head,typename... Tail>
void vout(Head&& h,Tail&&... t){cout << ' ' << h;vout(forward<Tail>(t)...);}
void out(){cout << endl;}
template<typename Head,typename... Tail>
void out(Head&& h,Tail&&... t){cout << h;vout(forward<Tail>(t)...);}

class UnionFind{
public:
	vector<ll> par;
	vector<ll> num;

	UnionFind(ll N):par(N),num(N){
		for(ll i=0;i<N;i++){
			par[i]=i;
			num[i]=1;
		}
	}

	ll root(ll x){
		if(par[x]==x){
			return x;
		}
		return par[x]=root(par[x]);
	}

	void unite(ll x,ll y){
		ll rx = root(x);
		ll ry = root(y);
		if (rx == ry) return;
		par[rx] = ry;
		num[ry] += num[rx];
	}

	bool same(ll x,ll y){
		ll rx = root(x);
		ll ry = root(y);
		return rx == ry;
	}

	ll getsize(ll x){
		return num[root(x)];
	}
};

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N=in(),M=in();
	UnionFind uf(N);
	REP(i,M){
		int u=in(),v=in();
		uf.unite(u,v);
	}
	int Q=in();
	REP(i,Q){
		int u=in(),v=in();
		out(uf.same(u,v)?"yes":"no");
	}

	return 0;
}