7.5 KiB
title |
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Steamroller |
Remember to use Read-Search-Ask
if you get stuck. Try to pair program and write your own code
Problem Explanation:
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.
Relevant Links
Hint: 1
You need to check if an element is an array or not.
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Hint: 2
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 [[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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Hint: 3
You will definitely need recursion or another way to go beyond two level arrays to make the code flexible and not hard-coded to the answers needed. Have fun!
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Spoiler Alert!
Solution ahead!
Basic Code Solution:
function steamrollArray(arr) {
var flattenedArray = [];
// Create function that adds an element if it is not an array.
// If it is an array, then loops through it and uses recursion on that array.
var flatten = function(arg) {
if (!Array.isArray(arg)) {
flattenedArray.push(arg);
} else {
for (var a in arg) {
flatten(arg[a]);
}
}
};
// Call the function for each element in the array
arr.forEach(flatten);
return flattenedArray;
}
// test here
steamrollArray([1, [2], [3, [[4]]]]);
Code Explanation:
- Create a new variable to keep flattened arrays.
- 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.
- 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.
- Invoke the function, the first time you will always pass it an array, so it always fall in to the isArray branch
- Return the flattened array.
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Intermediate Code Solution:
function steamrollArray(arr) {
let flat = [].concat(...arr);
return flat.some(Array.isArray) ? steamrollArray(flat) : flat;
}
flattenArray([1, [2], [3, [[4]]]]);
Code Explanation:
- Use spread operator to concatenate each element of
arr
with an empty array - Use
Array.some()
method to find out if the new array contains an array still - If it does, use recursion call
steamrollArray
again, passing in the new array to repeat the process on the arrays that were deeply nested - If it does not, return the flattened array
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Advanced Code Solution:
function steamrollArray(arr) {
return arr.toString()
.replace(',,', ',') // "1,2,,3" => "1,2,3"
.split(',') // ['1','2','3']
.map(function(v) {
if (v == '[object Object]') { // bring back empty objects
return {};
} else if (isNaN(v)) { // if not a number (string)
return v;
} else {
return parseInt(v); // if a number in a string, convert it
}
});
}
Code Explanation:
- 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.
- We replace the double comma with one, then split it back into an array.
- map through the array and fix object values and convert string numbers to regular numbers.
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See
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for reference.