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Tính Tiền Phòng/Kh.java
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

public class Kh implements Comparable<Kh> {
    private String id,name,room;
    private int stay;
    private Integer money;

    public Kh(int i, String name, String room, String dayIn, String dayOut, String sub) throws ParseException{
        this.id = String.format("KH%02d", i);
        this.room = room;
        int dongia;
        String tmp = room.substring(0,1);
        if(tmp.equals("1")) dongia = 25;
        else if(tmp.equals("2")) dongia = 34;
        else if(tmp.equals("3")) dongia = 50;
        else dongia = 80;
        this.name = chuanhoa(name);
        this.stay = setStay(dayIn, dayOut) +1;
        this.money = stay*dongia + Integer.parseInt(sub);
    }

    private Integer setStay(String dayIn, String dayOut) throws ParseException{
        int res;
        Date den = new SimpleDateFormat("dd/MM/yyyy").parse(dayIn);
        Date di = new SimpleDateFormat("dd/MM/yyyy").parse(dayOut);
        res = (int) ((di.getTime() - den.getTime())/(1000*3600*24));
        return res;
    }

    private String chuanhoa(String a){
        String res="";
        String[] tmp = a.trim().toLowerCase().split("\\s+");
        for(String i : tmp){
            String tmp3 = i.toUpperCase();
            char x = tmp3.charAt(0);
            String tmp2 = "";
            tmp2 =tmp2 + x ;
            for(int j = 1; j < i.length(); j++) tmp2= tmp2 + i.charAt(j) ;
            res = res + tmp2 + " ";
        }
        return res;
    }

    public int compareTo(Kh a){
        return -this.money.compareTo(a.money);
    }

    public String toString(){
        return id + " " + name + room + stay + " " + money;
    }
}
Tính Tiền Phòng/Main.java
import java.io.*;
import java.text.ParseException;
import java.util.*;

public class Main{
    public static void main(String[] args) throws IOException,FileNotFoundException,ClassNotFoundException,ParseException {
        Scanner sc = new Scanner(new File("KHACHHANG.in"));
        int t = Integer.parseInt(sc.nextLine());
        List<Kh> res = new ArrayList<>();
        for(int i = 1; i <= t; i ++){
            res.add( new Kh(i, sc.nextLine(), sc.nextLine(), sc.nextLine(), sc.nextLine(), sc.nextLine()));
        }
        res.sort(null);
        for(Kh a : res){
            System.out.println(a);
        }
    }
}