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<iostream>
#include<vector>
#include<stack>
using namespace std;
#define max 100000
#define 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>
#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 <iostream>
#include <vector>
#include <set>

using namespace std;

vector<set<int>> A;

bool dfs(int s, int t) {
    auto& S = A[s];
    if (S.find(t) != S.end()) {
        return true;
    }
    for (auto it = S.begin(); it != S.end(); ++it) {
        if (*it != t) {
            auto i = *it;
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

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

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y) || dfs(y, x)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
#include <stack>
#include <map>
#define FOR(i,b,e) for(int i=b;i<e;i++)
#define REP(i,n) FOR(i,0,n)
using namespace std;

const int N = 10000;
int n, m, q;
int M[N][N];
bool V[N];

int bfs(int u, int v) {
  int s;
  queue<int> q;
  REP(i, n) V[i] = false;

  s = u;
  q.push(s);
  V[s] = true;

  while (!q.empty() && !V[v]) {
    s = q.front(); q.pop();
    REP(i, n) {
      if (M[s][i] == 1 && !V[i]) {
        q.push(i);
        V[i] = true;
      }
    }
  }

  return V[v];
}

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

  REP(i, n) {
    REP(j, n) {
      M[i][j] = 0;
    }
  }

  cin >> n >> m;
  REP(i, m) {
    int u, v;
    cin >> u >> v;
    M[u][v] = M[v][u] = 1;
  }

  cin >> q;
  REP(i, q) {
    int u, v;
    string answer;
    cin >> u >> v;
    answer = bfs(u, v) ? "yes" : "no";
    cout << answer << endl;
  }
}

C++: 
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<stack>
#include<queue>
#include<vector>
#include<algorithm>
#include<string>
#include<iostream>
using namespace std;

int n,m,q;
static const int N=100005;
vector<int> G[N];
void branch(int a,int b){
    G[a].push_back(b);
    G[b].push_back(a);
}
int color[N];
void dfs(int r,int c){
    stack<int>s;
    s.push(r);
    while(!s.empty()){
        int u=s.top();s.pop();color[u]=c;
        for(int i=0;i<G[u].size();i++){
            if(color[G[u][i]]==0)s.push(G[u][i]);
        }
    }
}
void assigncolor(){
    int id=1;
    for(int u=0;u<n;u++){
        if(color[u]==0){
            dfs(u,id);
            id++;
        }
    }
}
void check(int a,int b){
    if(color[a]==color[b])printf("yes");
    else printf("no");
    printf("\n");
}
int main() {
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        int a,b;cin>>a>>b;
        branch(a,b);
    }
    assigncolor();
    cin>>q;
    for(int i=1;i<=q;i++){
        int a,b;cin>>a>>b;check(a,b);
    }
    return 0;
}