freeCodeCamp/curriculum/challenges/en/08-coding-interview-prep/project-euler/problem-19-counting-sundays.en.md

---
id: 5900f37f1000cf542c50fe92
challengeType: 5
title: 'Problem 19: Counting Sundays'
---

## 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>
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
- text: '<code>countingSundays(1943, 1946)</code> should return 6.'
  testString: 'assert.strictEqual(countingSundays(1943, 1946), 6, ''<code>countingSundays(1943, 1946)</code> should return 6.'');'
- text: '<code>countingSundays(1995, 2000)</code> should return 9.'
  testString: 'assert.strictEqual(countingSundays(1995, 2000), 9, ''<code>countingSundays(1995, 2000)</code> should return 9.'');'
- text: '<code>countingSundays(1901, 2000)</code> should return 171.'
  testString: 'assert.strictEqual(countingSundays(1901, 2000), 171, ''<code>countingSundays(1901, 2000)</code> should return 171.'');'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function countingSundays(firstYear, lastYear) {
  // Good luck!
  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 = 1; month <= 12; month++) {
      const thisDate = new Date(year, month, 1);
      if (thisDate.getDay() === 0) {
        sundays++;
      }
    }
  }
  return sundays;
}
```

</section>