Freecodecamp's Advanced Algorithm Scripting Challenge

No repeats please

/*
Return the number of total permutations of the provided string that don't have repeated consecutive letters. Assume that all characters in the provided string are each unique.

For example, aab should return 2 because it has 6 total permutations (aab, aab, aba, aba, baa, baa), but only 2 of them (aba and aba) don't have the same letter (in this case a) repeating.
*/

function permAlone(str) {
  var regex = /(.)\1+/g;

  var arr = str.split(''), permutations = [], temp;

  if (str.match(regex) !== null && str.match(regex)[0] === str) return 0;

  function swap(a, b) {
    temp = arr[a];
    arr[a] = arr[b];
    arr[b] = temp;
  }

  function generate(int) {
    if (int === 1) {
      permutations.push(arr.join(''));
    } else {
      for (var i = 0; i != int; ++i) {
        generate(int - 1);
        swap(int % 2 ? 0 : i, int - 1);
      }
    }
  }

  generate(arr.length);

  var filtered = permutations.filter(function(string) {
    return !string.match(regex);
  });

  return filtered.length;
}

permAlone('aab');