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 mx=100000;
static const int nil=-1;

int n;
vector<int>g[mx];
int color[mx];

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 i=0;i<n;i++)
		if(color[i]==nil)dfs(i,id++);
}
int main(int argc, char *argv[]) {
	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 <cassert>
#include <queue>

const int M = 10000000;

void connected_components(
  std::vector<std::vector<int> >& adj_list,
  std::vector<int>& component_numbers,
  int root, int current_component){
  assert(component_numbers[root] == M);

  std::queue<int> target_q;
  target_q.push(root);
  component_numbers[root] = current_component;
  // dist_q.push(0;)
  while(!target_q.empty()){
    int vtx = target_q.front(); target_q.pop();
    for(int const&  u : adj_list[vtx]){
      if(component_numbers[u] == M){
        target_q.push(u);
        component_numbers[u] = current_component;
      }
    }
  }
}

int main(int argc, char const *argv[]) {
  int n, m, q;
  std::cin >> n;
  std::cin >> m;

  std::vector<std::vector<int> > adj_list(n);

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

  std::vector<int> component(n, M);

  for (size_t i = 0; i < n; i++) {
    if(component[i] == M){
      connected_components(adj_list, component, i, i);
    }
  }

  std::cin >> q;
  for(size_t i =0; i < q; i++){
    int a, b;
    std::cin >> a;
    std::cin >> b;
    bool in_same_component = (component[a] == component[b]);
    std::cout << (in_same_component ? "yes" : "no") << std::endl;
  }
  

  return 0;
}

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

using namespace std;


const int MAX_N = 1000000;
int par[MAX_N];

//syokika
void init(int n){
  for(int i = 0; i < n; i++) par[i] = i;
}

//kinonewomotomeru
int root(int x){
  if(par[x] == x){
    return x;
  }else{
    return par[x] = root(par[x]);
  }
}

//hanntei
bool same(int x, int y){
  return root(x) == root(y);
}

void unite(int x, int y){
  x = root(x);
  y = root(y);
  if(x == y) return;

  par[x] = y;
}

int main(void){

  int n, m;
  cin >> n >> m;

  vector<int> adj[n];

  //syokika
  init(n);

  //heigou
  for(int i = 0; i < m; i++){
    int s, t; cin >> s >> t;
    unite(s, t);
  }

  int q; cin >> q;

  for(int i = 0; i < q; i++){
    int s, t; cin >> s >> t;
    if(same(s, 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;

vector<int> G[MAX];
int n;
int color[MAX];

void dfs(int v, int id)
{
    stack<int> S;
    S.push(v);
    color[v] = id;
    int u;
    while (!S.empty()) {
        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] = id;
                S.push(v);
            }
        }
    }
}

void assign_color()
{
    int id = 1;
    for (int i = 0; i < n; i++) {
        color[i] = NIL;
    }
    for (int i = 0; i < n; i++) {
        if (color[i] == NIL) {
            dfs(i, id++);
        }
    }
}

int main(int argc, char const *argv[])
{
    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_color();

    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 <stdio.h>
#include <stack>
#include <vector>

using namespace std;
const int nil = -1;

int total, n, m, q;

vector<int>* vecs;
typedef int Comm;
Comm* comms;

void find_connection(int from){
	stack<int> stk;
	stk.push(from);

	while(stk.size()){
		int top = stk.top();
		comms[top] = from;
		for(int i=0, sz=vecs[top].size(); i<=sz; ++i){
			if(i==sz){
				stk.pop();
				break;
			}
			if(comms[vecs[top][i]] == nil){
				stk.push(vecs[top][i]);
				break;
			}
		}
	}
}

int main()
{
	scanf("%d %d",&n,&m);
	vecs = new vector<int> [n];
	comms = new Comm [n];

	for(int i=0; i<n; ++i){
		comms[i] = nil;
	}

	for(int i=0; i<m; ++i){
		int id, f;
		scanf("%d %d",&id,&f);
		vecs[id].push_back(f);
		vecs[f].push_back(id);
	}

	scanf("%d",&q);
	for(int i=0; i<q;++i){
		int from, to;
		scanf("%d %d",&from,&to);
		if(comms[from]==nil && comms[to]==nil){
			find_connection(from);
			if(comms[from] == comms[to]){
				cout << "yes" << endl;
			}
			else{
				cout << "no" << endl;
			}
		}
		else if(comms[from] == comms[to]){
			cout << "yes" << endl;
		}
		else{
			cout << "no" << endl;
		}
	}

	delete[] comms;
	delete[] vecs;

	return 0;
}