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<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<tuple>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;

typedef pair<int, int> P;

void dfs(int s, int group, int n, vector<vector<int>> v, vector<int> &used) {
	used[s] = group;
	int k = v[s].size();
	REP(l, k) {
		int j = v[s][l];
		if (!used[j]) {
			dfs(j, group, n, v, used);
		}
	}
}

void divide(int n, vector<vector<int>> v, vector<int> &used) {
	int s = 0;
	int group = 1;
	while (s < n) {
		dfs(s, group++, n, v, used);
		while (s < n && used[s]) s++;
	}
}

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

	int n, m;
	cin >> n >> m;
	vector<vector<int>> v(n);
	REP(i, m) {
		int s, t;
		cin >> s >> t;
		v[s].push_back(t);
		v[t].push_back(s);
	}
	vector<int> used(n, 0);
	divide(n, v, used);
	int q;
	cin >> q;
	REP(i, q) {
		int s, t;
		cin >> s >> t;
		if (used[s] == used[t]) cout << "yes\n";
		else cout << "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 <vector>
using namespace std;

const int MAX = 100000;
vector<int> friends[MAX + 1];
int groups[MAX + 1];

void dfs(int id, int gid) {
  if (groups[id] != -1) return;
  groups[id] = gid;

  int l = friends[id].size();
  for (int i = 0; i < l; i++) {
    dfs(friends[id][i], gid);
  }
}

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

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

  int a, b, q;
  int gid = 0;

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

  for (int i = 0; i < n; i++) groups[i] = -1;

  for (int i = 0; i < n; i++) {
    if (groups[i] == -1) dfs(i, gid++);
  }

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

  for (int i = 0; i < n; i++) {
    cout << i << ":" << groups[i] << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<queue>

const static int MAX = 100000;
int color[MAX];
int group_color;
std::vector<int> A[MAX];

int search(int o){
    if(color[o] != 0){
	return 0;
    }
    std::queue<int> qu;
    qu.push(o);
    color[o] = group_color;
    while(!qu.empty()){
	int cur = qu.front();
	qu.pop();
	for(int i = 0; i < A[cur].size(); i++){
	    if(color[A[cur][i]] == 0){
		qu.push(A[cur][i]);
	    	color[A[cur][i]] = group_color;
	    }
	}
    }
    return 0;
}

int main(void){
    int n, m, s, t, q;

    std::cin >> n >> m;
    for(int i = 0; i < m; i++){
	std::cin >> s >> t;
	A[s].push_back(t);
	A[t].push_back(s);
    }
    for(int i = 0; i < n; i++){
        color[i] = 0;
    }
    group_color = 1;
    for(int i = 0; i < n; i++){
	search(i);
	group_color++;
    }

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

    return 0;
}

C++: #include <iostream>
#include <queue>
using namespace std;
struct Node{
    int u;
    vector<int> fri;
    bool flag;
};
queue<Node> refresh(queue<Node> que,Node node[],int n){
    while(!que.empty()){
        cout << que.front().u <<" \n";
        que.pop();
    }
    for(int i=0; i<n; i++)
        node[i].flag=false;

    return que;
}

int main(){
    int n,m,s,t;
    Node node[100000];
    cin >> n >> m;
    for(int i=0; i<n; i++)
        node[i].u=i;

    for(int i=0; i<m; i++){
        cin >> s >> t;

        node[s].fri.push_back(t);
        node[t].fri.push_back(s);
    }

    queue<Node> que;
    refresh(que,node,n);

    int q;
    cin >> q;

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

        node[s].flag=true;
        que.push(node[s]);

        while(!que.empty() && !answer[i]){
         Node fro = que.front();

         for(int j=0; j<fro.fri.size(); j++){
            int x = fro.fri[j];
  
            if(x==t){
                answer[i]=true;
                break;
            }

            if(!node[x].flag){
                node[x].flag=true;
                que.push(node[x]);
            }
         }

          que.pop();
        }

        que=refresh(que,node,n);
    }

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