92 lines
2.4 KiB
Markdown
92 lines
2.4 KiB
Markdown
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---
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id: 5cd9a70215d3c4e65518328f
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title: Use Recursion to Create a Countdown
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challengeType: 1
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---
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## Description
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<section id='description'>
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Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.
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</section>
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## Instructions
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<section id='instructions'>
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We have defined a function called <code>countdown</code> with two parameters. The function should take an array in the <code>myArray</code> parameter and append the numbers n through 1 based on the <code>n</code> parameter.
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For example, calling this function with <code>n = 5</code> will pad the array with the numbers <code>[5, 4, 3, 2, 1]</code> inside of it.
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Your function must use recursion by calling itself and must not use loops of any kind.
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</section>
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## Tests
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<section id='tests'>
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``` yml
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tests:
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- text: After calling <code>countdown(myArray, -1)</code>, myArray should be empty.
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testString: assert.isEmpty(padArray([], -1));
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- text: After calling <code>countdown(myArray, 10)</code>, myArray should contain <code>[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]</code>
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testString: assert.deepStrictEqual(padArray([], 10), [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);
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- text: After calling <code>countdown(myArray, 5)</code>, myArray should contain <code>[5, 4, 3, 2, 1]</code>
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testString: assert.deepStrictEqual(padArray([], 5), [5, 4, 3, 2, 1]);
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- text: Your code should not rely on any kind of loops (<code>for</code> or <code>while</code> or higher order functions such as <code>forEach</code>, <code>map</code>, <code>filter</code>, or <code>reduce</code>.).
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testString: assert(!removeJSComments(code).match(/for|while|forEach|map|filter|reduce/g));
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- text: You should use recursion to solve this problem.
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testString: assert(removeJSComments(countdown.toString()).match(/countdown\s*\(.+\)\;/));
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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//Only change code below this line
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function countdown(myArray, n){
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return;
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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const removeJSComments = str => str.replace(/\/\*[\s\S]*?\*\/|\/\/.*$/gm, '');
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function padArray(arr, n){
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countdown(arr, n);
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return arr;
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}
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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//Only change code below this line
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function countdown(myArray, n){
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if(n <= 0){
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return;
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}
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else{
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myArray.push(n);
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countdown(myArray, n - 1);
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}
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}
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```
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</section>
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