77 lines
1.7 KiB
Markdown
77 lines
1.7 KiB
Markdown
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---
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id: 5900f37f1000cf542c50fe92
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title: 'Problem 19: Counting Sundays'
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challengeType: 5
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forumTopicId: 301827
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dashedName: problem-19-counting-sundays
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---
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# --description--
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You are given the following information, but you may prefer to do some research for yourself.
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<ul>
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<li>1 Jan 1900 was a Monday.</li>
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<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>
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<li>A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.</li>
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</ul>
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How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
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# --hints--
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`countingSundays(1943, 1946)` should return a number.
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```js
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assert(typeof countingSundays(1943, 1946) === 'number');
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```
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`countingSundays(1943, 1946)` should return 6.
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```js
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assert.strictEqual(countingSundays(1943, 1946), 6);
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```
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`countingSundays(1995, 2000)` should return 10.
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```js
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assert.strictEqual(countingSundays(1995, 2000), 10);
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```
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`countingSundays(1901, 2000)` should return 171.
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```js
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assert.strictEqual(countingSundays(1901, 2000), 171);
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```
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# --seed--
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## --seed-contents--
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```js
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function countingSundays(firstYear, lastYear) {
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return true;
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}
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countingSundays(1943, 1946);
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```
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# --solutions--
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```js
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function countingSundays(firstYear, lastYear) {
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let sundays = 0;
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for (let year = firstYear; year <= lastYear; year++) {
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for (let month = 0; month <= 11; month++) {
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const thisDate = new Date(year, month, 1);
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if (thisDate.getDay() === 0) {
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sundays++;
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}
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}
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}
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return sundays;
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}
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```
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