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-2.js

const isPermutation = (s1, s2) => {
  if(s1.length != s2.length) return false;

  let count = new Map();
  for (let i = 0; i < s1.length; ++i) {
    count.set(s1[i], count.get(s1[i]) + 1 || 1); 
  }
  
  for(let j = 0; j < s2.length; ++j) {
    let num = count.get(s2[j]);
    if (!num) return false;
    if (num === 1) count.delete(s2[j]);
    else count.set(s2[j], num - 1);
  }
  
  return count.size === 0;
}

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);