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++: #define _CRT_SECURE_NO_DEPRECATE
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <set>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
const int         N_MAX = 100000 + 2;
vector<int>       G[N_MAX];
int               n, m;
int               Q;
int               color[N_MAX];

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

int main() {
    while (scanf("%d%d", &n, &m) != EOF) {
        memset(color, 0, sizeof(color));
        for (int i = 0; i < n; i++) {
            G[i].clear();
        }
        for (int i = 0; i < m; i++) {
            int from, to;
            scanf("%d%d", &from, &to);
            G[from].push_back(to);
            G[to].push_back(from);
        }
        int c = 1;
        for (int i = 0; i < n; i++) {
            if (!color[i]) {
                dfs(i, c);
                c++;
            }
        }

        scanf("%d", &Q);
        for (int i = 0; i < Q; i++) {
            int from, to;
            scanf("%d%d", &from, &to);
            if (color[from] == color[to])
                puts("yes");
            else
                puts("no");
        }
    }

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#define Lens 100005

using namespace std;
int n, m, q;
vector<int> A[Lens];
queue<int>	Q;
char c[Lens], d[Lens];

int Find(int s, int t)
{
	Q.push(s);
	c[s] = 'g';
	while (!Q.empty())
	{
		s = Q.front();
		Q.pop();
		c[s] = 'g';
		for (int j = 0; j < A[s].size(); j++)
		{
			if (c[A[s][j]] == 'w')
				Q.push(A[s][j]);
			if (A[s][j] == t)
			{
				return 1;
			}
		}
	}
	return 0;
}

int main()
{
	cin >> n >> m;
	for (int i = 0; i < m; i++)
	{
		int s, t;
		cin >> s >> t;
		d[s] = d[t] = 'w';
		A[s].push_back(t);
		A[t].push_back(s);
	}
	cin >> q;
	for (int i = 0; i < q; i++)
	{
		while (!Q.empty())
			Q.pop();
		for (int j = 0; j < n; j++)
			c[j] = d[j];
		int s, t;
		cin >> s >> t;
		if (Find(s, t))
			cout << "yes" << endl;

		else
			cout << "no" << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <stack>
#define MAX 100001
using namespace std;
vector<int> v[MAX];
int color[MAX];

void dfs(int x,int value){
	stack<int> s;
	s.push(x);
	color[x] = value;
	while(!s.empty()){
		int u = s.top();
		s.pop();
		for(int i = 0;i < v[u].size();i++){
			int a = v[u][i];
			if(color[a] == -1){
				color[a] = value;
				s.push(a);
			}
		}
	}
}

int main(){
	int n,m,q,x,y,value;
	cin >> n >> m;
	for(int i = 0;i < m;i++){
		cin >> x >> y;
		v[x].push_back(y);
		v[y].push_back(x);
	}

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

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

C++: #include <iostream>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

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

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

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

void dfs(int v, int id){
    stack<int> s;
    s.push(v);
    color[v]=id;

    while(!s.empty()){
        int u=s.top(); s.pop();
        for(int i=0; i<G[u].size(); i++){
            int v1=G[u][i];
            if(color[v1]==NIL){
                color[v1]=id;
                s.push(v1);
            }    
        }
    }
}

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); id++;
        }
    }
}

int main(void){
    int m; cin >> n >> m;

    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);
    }

    assignColor();

    int q; cin >> q;
    for(int i=0; i<q; i++){
        int s,t; scanf("%d %d", &s, &t);
        if(color[s]==color[t]) printf("yes\n");
        else printf("no\n");
    }

    return 0;
}

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

bool search(vector<int> member,int x){
  for(int i=0; i<member.size(); i++){
    if(member[i] == x)
      return true;
  }
    return false;
}
vector<int> update(vector<int> mother,vector<int> children,int join[],int a,int b){
  mother.push_back(b);
  join[b] = join[a];
  for(int i=0; i<children.size(); i++){
    int num=children[i];
    mother.push_back(num);
    join[num] = join[a];
  }

  return mother;
}
int main(){
  int n,m,join[100000],s,t;
  vector<int> group[100000];
  cin >> n >> m;

  for(int i=0; i<n; i++)
    join[i] = i;
    
  for(int i=0; i<m; i++){
    cin >> s >> t;
    bool flag = search(group[join[t]],s);

    if(!flag){
      int x = join[t];
      int y = join[s];

      if(x!=t || !group[x].empty())
	group[x] = update(group[x],group[y],join,x,y);


      else{
	group[y].push_back(t);
	join[x] = y;
      }
    }

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

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