CitrusByte_Flatten_Array_Exercise_Andrew_Deal_Solution.js

/*
Problem Description: 

  Given an array of integers AND/OR arbitrarily nested 
  arrays, return a single array of integers values only.

Input: <array>

Output: <array>

Time Complexity: O(n^2)

Space Complexity: O(n^2)

Edge cases and Assumptions:

- Empty arrays should be ignored unless its the base array - in which case return early.
- Undefined elements should be ignored
- Mutation of original array should be avoided

Pseudo Solution (recursion):
  If array is empty, return array => null case
  Initialize array-to-return
  Iterate through array
    If element is a number, push into array-to-return
    Else element is an array, recurse
      for each element returned by the recursive call, push into base array
  Return array-to-return
*/
const flattener = (toFlatten) => {
  if (toFlatten.length === 0) return toFlatten;
  let flattened = [];

  for (const numOrArray of toFlatten) {
    if (typeof numOrArray === 'number') flattened.push(numOrArray);
    else {
      for (const num of flattener(numOrArray)) {
        flattened.push(num);
      }
    }
  }

  return flattened;
};

// Helper to ensure correctness
const assertsArraysEqual = (arr1, arr2) => {
  if (arr1.length !== arr2.length) {
    return `INCORRECT: Array lengths do not match: Array 1 = ${arr1.length} | Array 2 = ${arr2.length}`;
  }
  for (const [index, element] of arr1.entries()) {
    if (element !== arr2[index]) {
      return `INCORRECT: Array 1 at position ${index} with value ${element} does not match Array 2's ${arr2[index]} | ${arr1} !== ${arr2}`;
    }
  }
  return `CORRECT: Array 1 and 2 match, flattening achieved!`;
};

/*
Sample Cases: 
  (Given Input) => (Expected Output)
  [] => []
  [1,2,3] => [1,2,3]
  [1,[2],[[3]] => [1,2,3],
  [[[4,5,6,],7],8],9] => [4,5,6,7,8,9]
  [[[[[[[[[[[4]]]]]]]]]]] => [4]
*/
console.log(assertsArraysEqual(flattener([1,2,3]),[1,2,3]));
console.log(assertsArraysEqual(flattener([]),[]));
console.log(assertsArraysEqual(flattener([1,[2],[[3]]]),[1,2,3]));
console.log(assertsArraysEqual(flattener([[[[4,5,6],7],8],9]),[4,5,6,7,8,9]));
console.log(assertsArraysEqual(flattener([[[[[[[[[[[4]]]]]]]]]]]),[4]));