CheckRearrangePalindrome.js

/**
 * What is a palindrome? https://en.wikipedia.org/wiki/Palindrome
 * Receives a string and returns whether it can be rearranged to become a palindrome or not
 * The string can only be a palindrome if the count of ALL characters is even or if the ONLY ONE character count is odd
 * Input is a string
 *
 **/

export const palindromeRearranging = (str) => {
 // check that input is a string
 if (typeof str !== 'string') {
 return 'Not a string'
 }
 // Check if is a empty string
 if (!str) {
 return 'Empty string'
 }

 // First obtain the character count for each character in the string and store it in an object.
 // Filter the object's values to only the odd character counts.
 const charCounts = [...str].reduce((counts, char) => {
 counts[char] = counts[char] ? counts[char] + 1 : 1
 return counts
 }, {})
 // If the length of the resulting array is 0 or 1, the string can be a palindrome.
 return (
 Object.values(charCounts).filter((count) => count % 2 !== 0).length <= 1
 )
}

// testing

// > palindromeRearranging('aaeccrr')
// true

// > palindromeRearranging('leve')
// false