135 lines
7.6 KiB
Markdown
135 lines
7.6 KiB
Markdown
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---
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title: Steamroller
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---
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 Remember to use <a>**`Read-Search-Ask`**</a> if you get stuck. Try to pair program  and write your own code 
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###  Problem Explanation:
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This problem seems simple but you need to make sure to flatten any array, regardless of the level which is what adds a bit of difficulty to the problem.
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#### Relevant Links
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* <a href='http://forum.freecodecamp.com/t/javascript-array-isarray/14284' target='_blank' rel='nofollow'>Array.isArray()</a>
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##  Hint: 1
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You need to check if an element is an array or not.
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> _try to solve the problem now_
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##  Hint: 2
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If you are dealing with an array, then you need flatten it by getting the value inside of the array. This means if you have <a href='https://forum.freecodecamp.com/images/emoji/emoji_one/speech_balloon.png?v=3 ":speech_balloon:"' target='_blank' rel='nofollow'>[4]] then instead of returning [4] you need to return 4\. If you get [[[4]]] then the same, you want the 4\. You can access it with arr[index1][index2] to go a level deeper.
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> _try to solve the problem now_
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## 
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**Solution ahead!**
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##  Basic Code Solution:
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function steamrollArray(arr) {
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var flattenedArray = [];
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// Create function that adds an element if it is not an array.
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// If it is an array, then loops through it and uses recursion on that array.
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var flatten = function(arg) {
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if (!Array.isArray(arg)) {
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flattenedArray.push(arg);
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} else {
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for (var a in arg) {
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flatten(arg[a]);
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}
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}
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};
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// Call the function for each element in the array
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arr.forEach(flatten);
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return flattenedArray;
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}
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// test here
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steamrollArray([1, [2], [3, [[4]]]]);
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 <a href='https://repl.it/CLnh/0' target='_blank' rel='nofollow'>Run Code</a>
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### Code Explanation:
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* Create a new variable to keep flattened arrays.
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* Create a function that will add non array elements to the new variable, and for the ones that are array it loops through them to get the element.
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* It does that by using recursion, if the element is an array then call the function again with a layer of array deeper to check if it is an array or not. if it is not then push that non-array element to the variable that gets returned. Otherwise, keep going deeper.
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* Invoke the function, the first time you will always pass it an array, so it always fall in to the isArray branch
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* Return the flattened array.
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#### Relevant Links
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* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-push/14298' target='_blank' rel='nofollow'>Array.push()</a>
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* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-foreach/14290' target='_blank' rel='nofollow'>Array.forEach()</a>
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##  Intermediate Code Solution:
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function steamrollArray(arr) {
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let flat = [].concat(...arr);
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return flat.some(Array.isArray) ? steamrollArray(flat) : flat;
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}
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flattenArray([1, [2], [3, [[4]]]]);
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 <a href='https://repl.it/CLni/0' target='_blank' rel='nofollow'>Run Code</a>
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### Code Explanation:
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* Use spread operator to concatenate each element of `arr` with an empty array
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* Use `Array.some()` method to find out if the new array contains an array still
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* If it does, use recursion call `steamrollArray` again, passing in the new array to repeat the process on the arrays that were deeply nested
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* If it does not, return the flattened array
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#### Relevant Links
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some' target='_blank' rel='nofollow'>Array.some</a>
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* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-concat/14286' target='_blank' rel='nofollow'>Array.concat</a>
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator' target='_blank' rel='nofollow'>Spread operator</a>
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator' target='_blank' rel='nofollow'>Ternary Operator (`condition ? a : b`)</a>
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##  Advanced Code Solution:
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function steamrollArray(arr) {
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return arr.toString()
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.replace(',,', ',') // "1,2,,3" => "1,2,3"
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.split(',') // ['1','2','3']
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.map(function(v) {
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if (v == '[object Object]') { // bring back empty objects
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return {};
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} else if (isNaN(v)) { // if not a number (string)
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return v;
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} else {
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return parseInt(v); // if a number in a string, convert it
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}
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});
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}
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 <a href='https://repl.it/CpDy/4' target='_blank' rel='nofollow'>Run Code</a>
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### Code Explanation:
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* First we turn the array to a string, which will give us a string of numbers seperated by a comma, double comma if there was an empty array and literal object text if there was an object, which we can fix it later in our if statement.
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* We replace the double comma with one, then split it back into an array.
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* map through the array and fix object values and convert string numbers to regular numbers.
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##  NOTES FOR CONTRIBUTIONS:
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*  **DO NOT** add solutions that are similar to any existing solutions. If you think it is **_similar but better_**, then try to merge (or replace) the existing similar solution.
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* Add an explanation of your solution.
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* Categorize the solution in one of the following categories — **Basic**, **Intermediate** and **Advanced**. 
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> See  <a href='http://forum.freecodecamp.com/t/algorithm-article-template/14272' target='_blank' rel='nofollow'>**`Wiki Challenge Solution Template`**</a> for reference.
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