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>
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 col) {
	color[r] = col;
	for (int i = 0; i < G[r].size(); i++) {
		int v = G[r][i];
		if (color[v] == NIL) {
			dfs(v, col);
		}
	}
}

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

int main() {
	int m, q, f, s;
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> f >> s;
		G[f].push_back(s);
		G[s].push_back(f);
	}

	assignColor();

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

C++: #include <cstdio>
#include <iostream>
#include <vector>

#define N 100000

using namespace std;

vector<int> G[N];
int color[N];

void dfs(int s,int c){
  color[s]=c;
  for(int i=0;i<G[s].size();i++){
    if(color[G[s][i]]!=c) dfs(G[s][i],c);
  }
}

int main(){
  int n,m;
  scanf("%d %d",&n,&m);
  for(int i=0;i<n;i++) color[i]=-1;
  for(int i=0;i<m;i++){
    int s,t;
    scanf("%d %d",&s,&t);
    G[s].push_back(t);
    G[t].push_back(s);
  }
  int q; scanf("%d",&q);
  for(int i=0;i<q;i++){
    int s,t;
    scanf("%d %d",&s,&t);
    dfs(s,i);
    if(color[s]==color[t]) cout << "yes\n";
    else cout << "no\n";
  }
}

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

const int maxm = 100000 + 5;
const int maxn = 100000 + 5;

struct Edge{
  int to,next;
} G[maxm<<1];

int head[maxn],cnt = 0;
int color[maxn];
bool vis[maxn];

void Insert(int u,int v){
  G[++cnt].next = head[u];
  G[cnt].to = v;
  head[u] = cnt;
}

void Dfs(int u,int c){
  vis[u] = true;
  color[u] = c;
  for (int e = head[u];e; e = G[e].next) {
    int v = G[e].to;
    if (!vis[v]) {
      Dfs(v,c);
    }
  }
}

int main(){
  int n,m;
  scanf("%d %d",&n,&m);
  for (int i=1;i<=m; i++) {
    int u,v;
    scanf("%d %d",&u,&v);
    Insert(u,v);
    Insert(v,u);
  }
  for (int i=1; i<=n; i++) {
    if (!vis[i]) {
      Dfs(i,i);
    }
  }
  int q;
  scanf("%d",&q);
  for(int i=1; i<=q; i++){
    int u,v;
    scanf("%d%d",&u,&v);
    if (color[u]==color[v]) {
      printf("yes\n");
    }
    else {
      printf("no\n");
    }
  }
}

C++: #include<iostream>
using namespace std;
#include<stdio.h>

int *P;

int root(int a)
{
    if(P[a] == a) return a;
    P[a] = root(P[a]);
    return P[a]; 
}

void join(int a, int b){ int x = root(a), y = root(b); x = P[y]; }

bool same(int a, int b){ return (root(a) == root(b) ? true : false); }

int main()
{
    int i, n, m, a, b, q;
    scanf("%d %d", &n, &m);
    P = new int [n];
    for(i = 0; i < n; i++) P[i] = i;

    for(i = 0; i < m; i++){ scanf("%d %d", &a, &b); join(a, b); }

    scanf("%d", &q);
    for(i = 0; i < q; i++){
        scanf("%d %d", &a, &b);
        if(same(a, b)){ printf("yes\n"); }else{ printf("no\n"); }
    }
    delete [] P;
    return 0; 
}

C++: // #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define Graph vector< vector<int> >
typedef long long ll;
typedef pair<int, int> P;
const int INF = 1000000007;

int main(){
    int N, M;
    cin >> N >> M;
    Graph G(N);
    rep(i, M){
        int s, t;
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }

    vector<int> connect(N, -1);

    for(int c = 0; c < N; c++){
        if(connect[c] != -1) continue;

        queue<int> que;
        connect[c] = c;
        que.push(c);

        while(!que.empty()){
            int v = que.front();
            que.pop();
            for(int i = 0; i < G[v].size(); i++){
                int v2 = G[v][i];
                if(connect[v2] != -1) continue;
                connect[v2] = c;
                que.push(v2);
            }
        }
    }

    int q;
    cin >> q;
    rep(i, q){
        int s, t;
        cin >> s >> t;
        if(connect[s] == connect[t]) cout << "yes" << endl;
        else cout << "no" << endl;
    }
}

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);
      }
    }
  }
}

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);
  }

  int id = 1;
  
  for ( int i = 0; i < n; ++i) {
    color[i] = NIL; //preset
  }
  
  for ( int u = 0; u < n; ++u) {
    if ( color[u] == NIL ) {
      dfs(u,id);
      id++;
    }
  }
  
  scanf("%d", &q);
  for ( int i = 0; i < q; ++i) {
    scanf("%d %d", &s, &t);
    if ( color[s] == color[t] ) {
      printf("yes\n");
    } else {
      printf("no\n");
    }
  }

  return (0);
}