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<bits/stdc++.h>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;
int n;
vector<int>G[MAX]; //頂点数を100000とする
                   //隣接リスト
int color[MAX];
void dfs(int r,int c){
  stack<int>S;
  S.push(r); //始点rをスタックに追加
  color[r]=c;//色を入れる
  while(!S.empty()){ //スタックがからでない間
    int u=S.top();
    S.pop(); //スタックから頂点uを取り出し訪問
    for(int i=0;i<G[u].size();i++){
      //頂点uに隣接する頂点vを探索
      int v=G[u][i];
      if(color[v]==NIL){
	color[v]=c;
	S.push(v); //id(色)は変わらない
      }
    }
  }
}
int main(){
  int m,s,t,q;
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>s>>t;
    G[s].push_back(t); //sからtへ辺
    G[t].push_back(s); //tからsへ辺
  }
  int id=1; //colorに入れる色(情報)
  for(int i=0;i<n;i++){
    color[i]=NIL; //全てにNIL
  }
  for(int u=0;u<n;u++){
    if(color[u]==NIL) dfs(u,id++); //id(色)にかぶりがないように
  }
  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>
using namespace std;
#include<stdio.h>

typedef struct box { int val; box *prev, *next; } box_t;

box_t* init()
{
    box_t* head = new box_t;
    head->val = -1;
    head->next = NULL;
    head->prev = NULL;
    return head;
}

box_t* make_tail(box_t* head)
{
    box_t* tail = new box_t;
    tail->val = -1;
    head->next = tail;
    tail->next = NULL;
    tail->prev = head;
    return tail;
}

bool isEmpty(box_t* head, box_t* tail)
{
    return (head->next == tail ? true : false);
}

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[3000][3000];
    int dist[3000];

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes\n"); }else{ printf("no\n"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

struct UnionFind{
    vector<int> par;
    UnionFind(int N) : par(N){
        for(int i = 0; i < N; i++){
            par[i] = -1;
        }
    }
    int root(int x){
        if(par[x] < 0) return x;
        else return par[x] = root(par[x]);
    }
    void unite(int x, int y){
        int rx = root(x);
        int ry = root(y);
        if(rx == ry) return;
        else{
            if(par[rx] > par[ry]) swap(rx, ry);
            par[rx] += par[ry];
            par[ry] = rx;
       }
    }
    bool same(int x, int y){
        return root(x) == root(y);
    }
    void check(){
        for(auto x : par){
            cout << x << " ";
        }
        cout << endl;
    }
};

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

    int n, m;
    cin >> n >> m;
    
    UnionFind uf(n);
    for(int i = 0; i < m; i++){
        int a, b;
        cin >> a >> b;
        uf.unite(a, b);
    }

    int q;
    cin >> q;
    for(int i = 0; i < q; i++){
        int s, t;
        cin >> s >> t;
        if(uf.same(s, t)){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }

    return 0;
}

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

int fri[100010];

int find(int x){
  if( fri[x] == x ) return x;
  else return fri[x] = find(fri[x]);
}

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

void uf_union(int x, int y){
  x = find(x);
  y = find(y);
  fri[x] = y;
}

int main(){

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

  // init
  for(int i=0; i<n; i++) fri[i] = i;

  //
  for(int i=0; i<m; i++){
    int u,v; scanf("%d %d",&u,&v);
    uf_union(u,v);
  }

  cin >> q;
  for(int i=0; i<q; i++){
    int u,v; scanf("%d %d",&u,&v);
    if( find(u) == find(v) ) printf("yes\n");
    else printf("no\n");
  }


}

C++: #include <stdio.h>
#include <string.h>
#define N 100010
int father[N];
int findfather(int x){
    if(x == father[x]) return x;
    else return findfather(father[x]);
}
int main(){
    int n, m;
    scanf("%d %d", &n, &m);
    for(int i = 0; i < n; i++) {
        father[i] = i;
    }
    for(int k = 0; k < m; k++){
        int a, b;
        scanf("%d %d", &a, &b);
        father[findfather(b)] = findfather(a);
    }

//    for(int i = 0; i < n; i++){
//        printf("i = %d father = %d\n", i, father[i]);
//    }
    int q;
    scanf("%d", &q);
    for(int k = 1; k <= q; k++){
        int x, y;
        scanf("%d %d", &x, &y);
        if(findfather(x) == findfather(y)) printf("yes\n");
        else printf("no\n");
    }
    return 0;
}