diff --git a/Project-Euler/Problem019.js b/Project-Euler/Problem019.js new file mode 100644 index 0000000000..5b488c7f96 --- /dev/null +++ b/Project-Euler/Problem019.js @@ -0,0 +1,48 @@ +/** + * Problem 19 - Counting Sundays + * + * @see {@link 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-one, + * Saving February alone, + * Which has twenty-eight, rain or shine. + * And on leap years, twenty-nine. + * A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400. + * How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)? + * + * @author ddaniel27 + */ +import { isLeapYear } from '../Maths/LeapYear' + +function problem19() { + let sundaysCount = 0 // Count of Sundays + let dayOfWeek = 2 // 1st Jan 1900 was a Monday, so 1st Jan 1901 was a Tuesday + + for (let year = 1901; year <= 2000; year++) { + for (let month = 1; month <= 12; month++) { + if (dayOfWeek === 0) { + // If it's a Sunday (0 is Sunday, 1 is Monday, ..., 6 is Saturday) + sundaysCount++ + } + + let daysInMonth = 31 + if (month === 4 || month === 6 || month === 9 || month === 11) { + // April, June, September, November + daysInMonth = 30 + } else if (month === 2) { + // February + daysInMonth = isLeapYear(year) ? 29 : 28 + } + + dayOfWeek = (dayOfWeek + daysInMonth) % 7 // Calculate the day of the week + } + } + + return sundaysCount +} + +export { problem19 } diff --git a/Project-Euler/test/Problem019.test.js b/Project-Euler/test/Problem019.test.js new file mode 100644 index 0000000000..8845e5a0ac --- /dev/null +++ b/Project-Euler/test/Problem019.test.js @@ -0,0 +1,8 @@ +import { problem19 } from '../Problem019.js' + +describe('checking sundays during the twentieth century', () => { + // Project Euler Challenge Check + test('result should be 171', () => { + expect(problem19()).toBe(171) + }) +})