Project-Euler-Problems/Problem_019.java at master · jwyce/Project-Euler-Problems · GitHub

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package euler;

import java.time.DayOfWeek;
import java.time.LocalDate;

public class Problem_019 {

	static int numberOfSundays() {
	    LocalDate start = LocalDate.of(1901, 1, 1);
        LocalDate end = LocalDate.of(2000, 12, 31);
        return numberOfSundays(start, end);
	}

	private static int numberOfSundays(LocalDate startDay, LocalDate endDay) {
		int numberOfSundays = 0;

		while(startDay.isBefore(endDay)) {
			startDay = startDay.plusMonths(1);
			if(startDay.getDayOfWeek() == DayOfWeek.SUNDAY) {
				numberOfSundays++;
			}
		}

		return numberOfSundays;
	}

//	private static int nonAPINumberOfSundays(int startDay, int startMonth, int startYear, int endDay, int endMonth, int endYear) {
//		int numberOfSundays = 0;
//		int knownMondayYear = 1900;
//		int currentDay = 0; 		// 1 = monday ... 0 = sunday
//		ArrayList<Integer> daysInMonths = new ArrayList<Integer>(12);
//		daysInMonths.add(31);
//		daysInMonths.add(28);
//		daysInMonths.add(31);
//		daysInMonths.add(30);
//		daysInMonths.add(31);
//		daysInMonths.add(30);
//		daysInMonths.add(31);
//		daysInMonths.add(31);
//		daysInMonths.add(30);
//		daysInMonths.add(31);
//		daysInMonths.add(30);
//		daysInMonths.add(31);
//
//		while(knownMondayYear <= endYear) {
//			for(int month = 0; month < daysInMonths.size(); month++) {
//				if(month == 1 && startYear % 4 == 0 && (startYear % 100 != 0 || startYear % 400 == 0) ) {		// leap year
//					currentDay = (currentDay + daysInMonths.get(month) + 1) % 7;
//				} else {
//					currentDay = (currentDay + daysInMonths.get(month)) % 7;
//				}
//
//				if(knownMondayYear >= startYear && month >= startMonth - 1) {		// start counting sundays
//					if((currentDay + 1) % 7 == 0) numberOfSundays++;
//				}
//			}
//			knownMondayYear++;
//		}
//
//		return numberOfSundays;
//	}

}