Some expert level JS challenges (according to Hackernoon post)

index.test.ts

export const getLenOfLongestSubstringWithoutRepeatingChars = (
  str: string,
): number => {
  // If the string is empty, return 0
  if (str.length === 0) {
    return 0;
  }

  // Start building a substring from the first character until we duplicate a character
  return str
    .split('')
    .reduce(
      (acc, char, index, origin) => {
        const lastI = acc.length - 1;

        // Either append to the last string in 'acc' or start a new one (if duplicate char)
        const lastString = acc[lastI];

        if (lastString.includes(char)) {
          // Append a new string that goes back to the last occurrence of the duplicate char (+ 1)
          return [...acc, str.slice(str.lastIndexOf(char, index - 1), index)];
        }

        acc[lastI] = lastString + char;
        return acc;
      },
      [''],
    )
    .sort((a, b) => b.length - a.length)[0].length;
};

export const restructureArrayNumsFirstLettersSecond = (
  numsAndLetters: (number | string)[],
  sorted = false,
) => {
  const nums = numsAndLetters.filter(
    (item) => typeof item === 'number',
  ) as number[];
  const letters = numsAndLetters.filter(
    (item) => typeof item === 'string',
  ) as string[];

  if (sorted) {
    return [...nums.sort((a, b) => a - b), ...letters.sort()];
  }

  return [...nums, ...letters];
};

index.ts

import { it, describe, expect, test } from 'vitest';
import {
  getLenOfLongestSubstringWithoutRepeatingChars,
  restructureArrayNumsFirstLettersSecond,
} from '.';

describe('getLenOfLongestSubstringWithoutRepeatingChars', () => {
  test('Find the length of the longest substring without repeating characters', () => {
    const input = 'abbbcabcdefef';
    const output = 6;

    expect(getLenOfLongestSubstringWithoutRepeatingChars(input)).toBe(output);
  });

  it('should return 0 for empty string', () => {
    const input = '';
    const output = 0;

    expect(getLenOfLongestSubstringWithoutRepeatingChars(input)).toBe(output);
  });
});

describe('restructureArrayNumsFirstLettersSecond (sorted 2)', () => {
  const input = [2, 'b', 4, 'd', 3, 'a', 'c', 'e', 5, 1];

  it('should restructure the array', () => {
    const output = [2, 4, 3, 5, 1, 'b', 'd', 'a', 'c', 'e'];

    expect(restructureArrayNumsFirstLettersSecond(input)).toEqual(output);
  });

  it('should restructure and sort the array', () => {
    const output = [1, 2, 3, 4, 5, 'a', 'b', 'c', 'd', 'e'];

    expect(restructureArrayNumsFirstLettersSecond(input, true)).toEqual(output);
  });
});