package com.mystuff.juststuff;

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.util.Arrays;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Palindrome {

  private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMddyyyy");

  public Set<LocalDate> countDatePalindromes(final LocalDate startDate, final LocalDate endDate) {
    final SortedSet<LocalDate> sortedDates = new TreeSet<>(Arrays.asList(startDate, endDate));
    return IntStream.rangeClosed(sortedDates.first().getYear(), sortedDates.last().getYear())
        .filter(Palindrome::isPalindromePossible)
        .mapToObj(Palindrome::createPalindrome)
        .filter(isDateInRange(sortedDates.first(), sortedDates.last()))
        .collect(Collectors.toCollection(TreeSet::new));
  }
  
  private static boolean isPalindromePossible(int year) {
      int monthFirstDigit = year % 10;
      return monthFirstDigit == 0 || monthFirstDigit == 1; 
  }

  private static LocalDate createPalindrome(final int year) {
    final String yearStr = String.valueOf(year);
    final String datePalindrome = new StringBuilder(yearStr).reverse().append(yearStr).toString();
    try {
      return LocalDate.parse(datePalindrome, formatter);
    } catch (final DateTimeParseException e) {}
    return null;
  }

  private static Predicate<LocalDate> isDateInRange(final LocalDate startDate, final LocalDate endDate) {
    return (date) -> !(date == null || date.isBefore(startDate) || date.isAfter(endDate));
  }
}

package com.mystuff.juststuff;

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Palindrome {

	private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMddyyyy");

	public Set<LocalDate> countDatePalindromes(final LocalDate startDate, final LocalDate endDate) {
		return IntStream.range(startDate.getYear(), endDate.getYear() + 1).mapToObj(Palindrome::createPalindrome)
				.filter(date -> isValidDate(date, startDate, endDate)).collect(Collectors.toCollection(TreeSet::new));
	}

	private static LocalDate createPalindrome(int year) {
		String yearStr = String.valueOf(year);
		String datePalindrome = new StringBuilder().append(yearStr).reverse().append(yearStr).toString();
		try {
			return LocalDate.parse(datePalindrome, formatter);
		} catch (DateTimeParseException e) {
			return null;
		}

	}

	private static boolean isValidDate(final LocalDate date, LocalDate startDate, LocalDate endDate) {
		if (date == null)
			return false;
		if (startDate.isEqual(date) || endDate.isEqual(date))
			return true;
		return startDate.isBefore(date) && endDate.isAfter(date) ||
				endDate.isBefore(date) && startDate.isAfter(date);
	}
}