solution: Project Euler Problem 19

Project-Euler/Problem019.js

@@ -0,0 +1,37 @@
+/*
+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)?
+*/
+
+export function countingSundays () {
+  let numberOfSundays = 0
+  let dow = 2
+
+  // The number od days in each month of the year
+  const months = [31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+
+  for (let y = 1901; y <= 2000; y++) {
+    // Calculate the number of Days in February this year
+    months[1] = 28 + ((y % 4 === 0 && y % 100 !== 0) || y % 400 === 0)
+
+    for (const month of months) {
+      dow = dow + (month % 7)
+
+      if (dow % 7 === 0) {
+        numberOfSundays++
+      }
+    }
+  }
+
+  return numberOfSundays
+}

Project-Euler/test/Problem019.test.js

@@ -0,0 +1,8 @@
+import { countingSundays } from '../Problem019.js'
+
+describe('checking Counting Sundays', () => {
+  // Project Euler Condition Check
+  test('Test Euler Condition', () => {
+    expect(countingSundays()).toBe(171)
+  })
+})