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fix(curriculum): Improved Use Recursion to Create a Countdown challenge (#37548)

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* fix: improved recursive challenge

* fix: rewording of two challenges

* fix: add code tags

Co-Authored-By: Tom <20648924+moT01@users.noreply.github.com>
This commit is contained in:
Randell Dawson
2019-12-02 08:58:07 -08:00
committed by Oliver Eyton-Williams
parent a6766127cc
commit 7454719334
3 changed files with 38 additions and 48 deletions
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58
curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/use-recursion-to-create-a-countdown.md
View File

@@ -8,15 +8,34 @@ forumTopicId: 305925
## Description
<section id='description'>
Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.
In a [previous challenge](/learn/javascript-algorithms-and-data-structures/basic-javascript/replace-loops-using-recursion), you learned how to use recursion to replace a for loop. Now, let's look at a more complex function that returns an array of consecutive integers starting with <code>1</code> through the number passed to the function.
As mentioned in the previous challenge, there will be a <dfn>base case</dfn>. The base case tells the recursive function when it no longer needs to call itself. It is a simple case where the return value is already known. There will also be a <dfn>recursive call</dfn> which executes the original function with different arguments. If the function is written correctly, eventually the base case will be reached.
For example, say you want to write a recursive function that returns an array containing the numbers <code>1</code> through <code>n</code>. This function will need to accept an argument, <code>n</code>, representing the final number. Then it will need to call itself with progressively smaller values of <code>n</code> until it reaches <code>1</code>. You could write the function as follows:
```javascript
function countup(n) {
if (n < 1) {
return [];
} else {
const countArray = countup(n - 1);
countArray.push(n);
return countArray;
}
}
console.log(countup(5)); // [ 1, 2, 3, 4, 5 ]
```
At first, this seems counterintuitive since the value of `n` <em>decreases</em>, but the values in the final array are <em>increasing</em>. This happens because the push happens last, after the recursive call has returned. At the point where `n` is pushed into the array, `count(n - 1)` has already been evaluated and returned `[1, 2, ..., n - 1]`.
</section>
## Instructions
<section id='instructions'>
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.
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.
We have defined a function called <code>countdown</code> with one parameter (<code>n</code>). The function should use recursion to return an array containing the integers <code>n</code> through <code>1</code> based on the <code>n</code> parameter. If the function is called with a number less than 1, the function should return an empty array.
For example, calling this function with <code>n = 5</code> should return the array <code>[5, 4, 3, 2, 1]</code>.
Your function must use recursion by calling itself and must not use loops of any kind.
</section>
@@ -26,13 +45,13 @@ Your function must use recursion by calling itself and must not use loops of any
``` yml
tests:
- text: After calling <code>countdown(myArray, -1)</code>, myArray should be empty.
testString: assert.isEmpty(padArray([], -1));
- text: After calling <code>countdown(myArray, 10)</code>, myArray should contain <code>[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]</code>
testString: assert.deepStrictEqual(padArray([], 10), [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);
- text: After calling <code>countdown(myArray, 5)</code>, myArray should contain <code>[5, 4, 3, 2, 1]</code>
testString: assert.deepStrictEqual(padArray([], 5), [5, 4, 3, 2, 1]);
- 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>.).
- text: <code>countdown(-1)</code> should return an empty array.
testString: assert.isEmpty(countdown(-1));
- text: <code>countdown(10)</code> should return <code>[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]</code>
testString: assert.deepStrictEqual(countdown(10), [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);
- text: <code>countdown(5)</code> should return <code>[5, 4, 3, 2, 1]</code>
testString: assert.deepStrictEqual(countdown(5), [5, 4, 3, 2, 1]);
- text: Your code should not rely on any kind of loops (<code>for</code>, <code>while</code> or higher order functions such as <code>forEach</code>, <code>map</code>, <code>filter</code>, and <code>reduce</code>).
testString: assert(!removeJSComments(code).match(/for|while|forEach|map|filter|reduce/g));
- text: You should use recursion to solve this problem.
testString: assert(removeJSComments(countdown.toString()).match(/countdown\s*\(.+\)\;/));
@@ -49,10 +68,10 @@ tests:
//Only change code below this line
function countdown(myArray, n){
function countdown(n){
return;
}
console.log(countdown(5)); // [5, 4, 3, 2, 1]
```
</div>
@@ -62,11 +81,6 @@ function countdown(myArray, n){
```js
const removeJSComments = str => str.replace(/\/\*[\s\S]*?\*\/|\/\/.*$/gm, '');
function padArray(arr, n){
countdown(arr, n);
return arr;
}
```
</div>
@@ -78,14 +92,8 @@ function padArray(arr, n){
```js
//Only change code below this line
function countdown(myArray, n){
if(n <= 0){
return;
}
else{
myArray.push(n);
countdown(myArray, n - 1);
}
function countdown(n){
return n < 1 ? [] : [n].concat(countdown(n - 1));
}
```

20
curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/use-recursion-to-create-a-range-of-numbers.english.md
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@@ -8,25 +8,7 @@ forumTopicId: 301180
## Description
<section id='description'>
In a [previous challenge](/learn/javascript-algorithms-and-data-structures/basic-javascript/replace-loops-using-recursion), you learned how to use recursion to replace a for loop. Now, let's look at a more complex function that returns an array of consecutive integers starting with <code>1</code> through the number passed to the function.
As mentioned in the previous challenge, there will be a <dfn>base case</dfn>. The base case tells the recursive function when it no longer needs to call itself. It is a simple case where the return value is already known. There will also be a <dfn>recursive call</dfn> which executes the original function with different arguments. If the function is written correctly, eventually the base case will be reached.
For example, say you want to write a recursive function that returns an array containing the numbers 1 through n. This function will need to accept an argument <code>n</code> representing the final number. Then it will need to call itself with progressively smaller values of <code>n</code> until it reaches 1. You could write the function as follows:
```js
function count(n) {
if (n === 1) {
return [1];
} else {
var numbers = count(n - 1);
numbers.push(n);
return numbers;
}
}
```
At first this is counterintuitive since the value of `n` <em>decreases</em>, but the values in the final array are <em>increasing</em>. This happens because the push happens last, after the recursive call has returned. At the point where `n` is pushed into the array, `count(n - 1)` has already been evaluated and returned `[1, 2, ..., n - 1]`.
Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.
</section>