Algorithms in Javascript: CTCI 1.4 Palindrome Permutation: Given a string, determine if it is a permutation of a palindrome.

ctci-1.4-is-string-a-permutation-1.js

const isPermutation = (s1, s2) => {

  if(s1.length != s2.length) return false;

  let count = {};
  for(let i=0; i < s1.length; i++) {
    count[s1[i]] = count[s1[i]] === undefined ? 1: count[s1[i]] + 1;
    count[s2[i]] = count[s2[i]] === 0 ? 0 : count[s2[i]] - 1;
  }
  
  for(let j in count){
    if(count[j] > 0)
      return false;
  }
  return true;
}

var a = isPermutation("paypalishiring", "palpayhiringis"); // true
var b = isPermutation("paypalishiring", "hiringpalsipay"); // true
var c = isPermutation("paypalishiring", "palpayhirising"); // true
var d = isPermutation("paypalishiring", "palpayhiringgg"); // false
console.log(a + ', ' + b + ', ' + c + ', ' + d);