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curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-19-counting-sundays.md

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+---
+id: 5900f37f1000cf542c50fe92
+challengeType: 5
+title: 'Problem 19: Counting Sundays'
+forumTopicId: 301827
+---
+
+## Description
+<section id='description'>
+
+You are given the following information, but you may prefer to do some research for yourself.
+
+<ul>
+  <li>1 Jan 1900 was a Monday.</li>
+  <li>Thirty days has September,<br>April, June and November.<br>All the rest have thirty-one,<br>Saving February alone,<br>Which has twenty-eight, rain or shine.<br>And on leap years, twenty-nine.</li>
+  <li>A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.</li>
+</ul>
+
+How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
+
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>countingSundays(1943, 1946)</code> should return a number.
+    testString: assert(typeof countingSundays(1943, 1946) === 'number');
+  - text: <code>countingSundays(1943, 1946)</code> should return 6.
+    testString: assert.strictEqual(countingSundays(1943, 1946), 6);
+  - text: <code>countingSundays(1995, 2000)</code> should return 10.
+    testString: assert.strictEqual(countingSundays(1995, 2000), 10);
+  - text: <code>countingSundays(1901, 2000)</code> should return 171.
+    testString: assert.strictEqual(countingSundays(1901, 2000), 171);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function countingSundays(firstYear, lastYear) {
+
+  return true;
+}
+
+countingSundays(1943, 1946);
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function countingSundays(firstYear, lastYear) {
+  let sundays = 0;
+
+  for (let year = firstYear; year <= lastYear; year++) {
+    for (let month = 0; month <= 11; month++) {
+      const thisDate = new Date(year, month, 1);
+      if (thisDate.getDay() === 0) {
+        sundays++;
+      }
+    }
+  }
+  return sundays;
+}
+```
+
+</section>