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2724 & 2619 - Sort By & Array.prototype.last

· 2 min read
Will Holmes

The problem statement​

Sort By​

Given an array arr and a function fn, return a sorted array sortedArr. You can assume fn only returns numbers and those numbers determine the sort order of sortedArr. sortedArray must be sorted in ascending order by fn output.

You may assume that fn will never duplicate numbers for a given array.

Array prototype last​

Write code that enhances all arrays such that you can call the array.last() method on any array and it will return the last element. If there are no elements in the array, it should return -1.

You may assume the array is the output of JSON.parse.

Understanding the problem​

Sort By​

Please return us a sorted array based upon the values generated via the fn() param, they will never return a duplicate number.

Array prototype last​

The question is asking us within the this scope of the array, please return us the last element or -1 if there are no elements.

Code​

Array prototype last​

Array.prototype.last = function () {
  return this.length === 0 ? -1 : this[this.length - 1];
};

Sort By​

type JSONValue =
  | null
  | boolean
  | number
  | string
  | JSONValue[]
  | { [key: string]: JSONValue };
type Fn = (value: JSONValue) => number;

function sortBy(arr: JSONValue[], fn: Fn): JSONValue[] {
  return arr.sort((a, b) => fn(a) - fn(b));
}

Key takeaways​

  1. Prototype functions hold the thing its extending within the this scope.
  2. The js sort prototype has a complexity of O(log n).