07_0_multidimensional-arrays.md

Multidimensional Arrays

Flattening Multidimensional Arrays

Another common challenge is to flatten multidimensional arrays. So, for the input [1, [2, [3 , [4]], [5]], 6] we should receive the output [1, 2, 3, 4, 5, 6]

The key is we don't know the depth of our array of arrays.

If you are thinking of using .flat(Infinity), even when it will work, probably your interviewer will not accept it as a valid answer.

Example:

const arr = [1, [2, [3 , [4]], [5]], 6]

console.log(arr.flat(Infinity))

Result: [1, 2, 3, 4, 5, 6]

Solution: recursion

function flatten(nestedArr) {
  const tempArr = [];
  
  
  (function flat(arr) {
    console.log('flat > nestedArr is', JSON.stringify(arr))
    arr.map((el) => {
      if (Array.isArray(el)) flat(el);
      else tempArr.push(el);
    });
  })(nestedArr);
  

  console.log('flatten > nestedArr is', JSON.stringify(nestedArr))
  
  return tempArr
}


const arr = [1, [2, [3 , [4]], [5]], 6]

console.log(flatten(arr))

Result:

flat > nestedArr is [1,[2,[3,[4]],[5]],6]
flat > nestedArr is [2,[3,[4]],[5]]
flat > nestedArr is [3,[4]]
flat > nestedArr is [4]
flat > nestedArr is [5]
flatten > nestedArr is [1,[2,[3,[4]],[5]],6]

[1, 2, 3, 4, 5, 6]

---

Sum

We have to SUM all the element in an array.

For an array with no sub-arrays: [1, 2, 3] the output should be 6

For an array with sub-arrays, for each sub-array we SUM and MULTIPLY by its depth So, for [1, [2, 3, [4, 5]] this would be the logic...

1
[2, 3, [4, 5]]
  2
  3
  [4, 5]
    4
    5

Or, with levels

Level 1...
1
[2, 3, [4, 5]]

  Level 2...
  2
  3
  [4, 5]

    Level 3...
    4
    5

Solution:

• Time complexity: O(n) (n is the total number of elements in the array plus number of sub-arrays, if we have 4 elements and 2 sub-arrays, n will be 6)
• Space complexity: O(d) (d is the greatest depth of the sub-arrays)

function mdArraySum(array, multiplier = 1) {
  let sum = 0
  for (let element of array) {
    if (Array.isArray(element)) sum += mdArraySum(element, multiplier + 1)
    else sum += element
  }
  return sum * multiplier
}

mdArraySum([1, [3,6], [-1, [-8, 1], 8]])
// -9