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Solving Two to One Codewars Problem in JS

The problem is about 2 strings to create a single string, all characters should be unique, and they should be sorted alphabetically in ascending order.

Problem: Take 2 strings s1 and s2 including only letters from a to z. Return a new sorted string (alphabetical ascending), the longest possible, containing distinct letters – each taken only once – coming from s1 or s2.

Examples:
a = "xyaabbbccccdefww"
b = "xxxxyyyyabklmopq"
longest(a, b) -> "abcdefklmopqwxy"

a = "abcdefghijklmnopqrstuvwxyz"
longest(a, a) -> "abcdefghijklmnopqrstuvwxyz"

In my mind, there are two ways to fix this problem:

  1. Use Object with keys of each characters of alphabet and check if string contains the character then store value true for that character in the object.
  2. Use Array of size all characters, but don’t store the character until they are present in the string. It would even result a sorted array.

Using Object

  1. Create an object with all character’s keys by default value should be false. Example: {a: false, b: false, …}
  2. Add/concatenate s1 and s2 strings to build a single string. Example (s3 = s1+s2)
  3. Split the string on empty character to make an array with each characters using this code: s3.split(“”)
  4. loop on s3Array for each characters and set true in object for the characters found.
  5. Create an empty array.
  6. Loop over the object keys and store the key in new array if the value is true.
  7. Join the new array to make string with this code: newArray.join(“”)
  8. Return the newString as answer.
function longest(s1, s2) {
  const alphabetArray = Array.from({ length: 26 }, (_, i) => [String.fromCharCode(97+i), false])
  const alphabetObject = Object.fromEntries(alphabetArray)
  const s3 = s1+s2;
  const s3Array = s3.split("");
  s3Array.forEach(char => {
    alphabetObject[char] = true;
  })
  let result = [];
  Object.keys(alphabetObject).forEach(key => {
    if(alphabetObject[key]) {
      result.push(key);
    }
  })

  return result.join("");
}

Using Array

  1. Create an empty array with 26 items space. Because alphabet do have 26 characters.
  2. Add/concat s1 and s2 strings to build a single string.
  3. Split the string on empty character to make an array with each characters using this code: s3.split(“”)
  4. loop on s3Array for each characters and for each character get their character code using this code: character.charCodeAt(0).
  5. Char Code will be from 97 (for character “a”) to 122 (for character “z”).
  6. Subtract 97 from the value of the character and store the character at the subtracted value index in array.
  7. Join the array on empty character to create a string.
function longest(s1, s2) {
  const alphabetArray = new Array(26);
  const s3 = s1+s2;
  const s3Array = s3.split("");
  s3Array.forEach(char => {
    const charCode = char.charCodeAt(0);
    alphabetArray[charCode-97] = char;
  })
  return alphabetArray.join("");
}

Link to problem: https://www.codewars.com/kata/5656b6906de340bd1b0000ac