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Spotify 'best before' test program solved
import java.util.Date;
import java.util.Scanner;
import java.util.LinkedList;
import java.util.Iterator;
import java.text.SimpleDateFormat;
public class BestBefore {
//Verify if it is a leap year
public static boolean isaleapyear (int year) {
boolean result=false;
if ((year%4==0)&&((year%100!=0)||(year%400==0))) { result=true; }
return result;
//Verify is generated date could be a valid date
public static boolean correctDate(String s_year, String s_month, String s_day) {
int year=Integer.parseInt(s_year),month=Integer.parseInt(s_month),day=Integer.parseInt(s_day);
int[] monthDays={0,31,28,31,30,31,30,31,31,30,31,30,31};
boolean result=true;
if (isaleapyear(year)) { monthDays[2]=29; }
if ((month<=0)||(month>12)) {
} else {
if ((day<=0)||(day>monthDays[month])) { result=false; }
return result;
//Transform input year in a four digit year
public static String extendedYear (String s_year) {
int year=0;
if (year<2000) { year=year+2000; }
return String.valueOf(year);
//Verify input string is correctly formated
public static boolean inputStringisCorrect(String line) {
int k=0,x=0,y=0,fourDigitYear=0;
String n_line;
boolean result=true;
n_line = new String(line.replaceAll("/", ""));
if ((n_line.length()+2)!=line.length()) {
} else {
String[] number = line.split("/");
for (int i=0;i<3;i++) {
if (number[i].length()==4) { fourDigitYear++; k=i; }
if (fourDigitYear>1){
} else {
if (fourDigitYear==1) {
switch(k) {
case 0: x=1; y=2; break;
case 1: x=0; y=2; break;
case 2: x=0; y=1; break;
if ((Integer.parseInt(number[k])<2000)||(Integer.parseInt(number[k])>2999)) { result=false; }
if ((number[x].length()<1)||(number[x].length()>2)) { result=false; }
if ((number[y].length()<1)||(number[y].length()>2)) { result=false; }
} else {
for (int i=0; i<3; i++) {
if ((number[i].length()<1)||(number[i].length()>2)) { result=false; }
return result;
public static void main(String[] args) {
try {
long value=0;
boolean anyDate=false;
int val1=0,val2=0,val3=0;
Date currentDate;
Date resultDate = new Date();
LinkedList<Date> listofDates = new LinkedList<Date>();
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd");
//Read initial date from the standard system input
Scanner sca = new Scanner(;
String line = sca.nextLine();
//Verify input string is correct
if (inputStringisCorrect(line)) {
String[] number = line.split("/");
//In each iteration we change the position of array elements to generate all possible date combinations (up to six)
for (int i=0;i<6;i++) {
switch (i) {
case 0: val1=0;val2=1;val3=2; break;
case 1: val1=0;val2=2;val3=1; break;
case 2: val1=1;val2=0;val3=2; break;
case 3: val1=1;val2=2;val3=0; break;
case 4: val1=2;val2=0;val3=1; break;
case 5: val1=2;val2=1;val3=0; break;
if (correctDate(extendedYear(number[val1]), number[val2], number[val3])) {
if (currentDate.getTime()>=value) { value=currentDate.getTime(); }
//Now, we got a list of valid dates. We're going to search on it to find the earliest one
Iterator<Date> iterator = listofDates.iterator();
currentDate = (Date);
if (currentDate.getTime()<=value) {
resultDate = currentDate;
//Finally, if there is any valid date, we show it in the required output format
if (anyDate) {
java.text.SimpleDateFormat sdf=new java.text.SimpleDateFormat("yyyy-MM-dd");
} else {
System.out.println(line+" is illegal");
} else {
//Input string is incorrect so we write an illegal message on standard output
System.out.println(line+" is illegal");
}catch (Exception e){
System.err.println("Error: " + e.getMessage());
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