Function Problem19

project_euler/problem_19/problem19.go:26–53

** * Problem 19 - Counting Sundays * @see https://projecteuler.net/problem=19 * * You are given the following information, * but you may prefer to do some research for yourself. * * 1 Jan 1900 was a Monday. * Thirty days has September, * April, June and November. * All the rest have thirty-o

()

 */

func Problem19() int {
	count := 0
	dayOfWeek := 2 // 1 Jan 1901 was a Tuesday

	for year := 1901; year <= 2000; year++ {
		for month := 1; month <= 12; month++ {
			if dayOfWeek == 0 {
				count++
			}

			daysInMonth := 31
			switch month {
			case 4, 6, 9, 11:
				daysInMonth = 30
			case 2:
				if IsLeapYear(year) {
					daysInMonth = 29
				} else {
					daysInMonth = 28
				}
			}

			dayOfWeek = (dayOfWeek + daysInMonth) % 7
		}
	}

	return count
}

func IsLeapYear(year int) bool {
	if year%4 == 0 {