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<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<numeric>
#include<map>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;
typedef pair<ll, ll> mp;

//Union-Find??¨

int par[100000];//?±????????????£???
vector<vector<int> >v(100000);

int find(int x){
	if(par[x]==x)return x;
	return par[x]=find(par[x]);//????????§????????§???
}

bool same(int x,int y){
	return find(x)==find(y);
}

void unify(int x,int y){
	x=find(x);
	y=find(y);
	if(x==y)return;
	par[x]=y;
}

int main(void){
	int n,m,f1,f2,q,s[10000],t[10000];
	cin>>n>>m;
	rep(i,n)par[i]=i;//union-find??¨????????????
	rep(i,m){
		cin>>f1>>f2;
		unify(f1,f2);
	}
	cin>>q;
	rep(i,q)cin>>s[i]>>t[i];//query
	rep(i,q)if(same(s[i],t[i])){
		cout<<"yes"<<endl;
	}else{
		cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <set>
#include <queue>
#include <vector>

void assignGroup(const std::vector<std::set<int>>& firend_relationships, std::vector<int>& group)
{
  int current_group = 1;
  std::queue<int> next_queue;
  std::set<int> searched_set;

  for (int i = 0; i < (int)firend_relationships.size(); ++i)
  {
    // Any group is the id assigned, then skip it
    if (searched_set.count(i) != 0)
      continue;

    group[i] = current_group;
    next_queue.push(i);

    while (!next_queue.empty())
    {
      // Remove from waiting list
      int current_id = next_queue.front();
      next_queue.pop();
      // Add to searched list
      searched_set.insert(current_id);

      // Add to waiting list which is not serached yet
      std::set<int>::const_iterator itr;
      for (itr = firend_relationships[current_id].begin();
           itr != firend_relationships[current_id].end();
           ++itr)
      {
        // Ignore searched ones
        if (searched_set.count(*itr) != 0)
          continue;

        group[*itr] = current_group;
        next_queue.push(*itr);
      }
    }

    // Assign the different group number
    ++current_group;
  }
}

bool isConnected(const int& id_from, const int& id_to, const std::vector<int>& group)
{
  return group[id_from] == group[id_to];
}

int main()
{
  int n, m;
  scanf("%d%d", &n, &m);

  std::vector<std::set<int>> firend_relationships;
  std::vector<int> group;
  firend_relationships.resize(n);
  group.resize(n);
  for (int i = 0; i < m; ++i)
  {
    int id1, id2;
    scanf("%d%d", &id1, &id2);
    firend_relationships[id1].insert(id2);
    firend_relationships[id2].insert(id1);
  }

  assignGroup(firend_relationships, group);

  int q;
  scanf("%d", &q);
  for (int i = 0; i < q; ++i)
  {
    int id1, id2;
    scanf("%d%d", &id1, &id2);
    if (isConnected(id1, id2, group))
      printf("yes\n");
    else
      printf("no\n");
  }

  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 <algorithm>
#include <cstdio>
#include <cmath>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <vector>
#include <cstdlib>
#include <list>
#define _USE_MATH_DEFINES
#include <math.h>

using namespace std;

static const int MAX = 100000;
static const int NIL = -1;

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

void assignColor();
void dfs(int r, int c);

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;
}

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++);
	}
		
}

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);
			}
		}
	}
}