worst-complexity-reorder-example.js

const isOrdered = arr => !arr.some((v, i) => v == arr[i + 1]);
function swap(alphabets, idx1, idx2) {
  var t = alphabets[idx1];
  alphabets[idx1] = alphabets[idx2];
  alphabets[idx2] = t;
  return alphabets;
}
function permute(alphabets, startIndex = 0, endIndex = alphabets.length - 1) {
  if (startIndex !== endIndex) {
    for (var i = startIndex; i <= endIndex; i++) {
      if (isOrdered(alphabets)) return true;
      swap(alphabets, startIndex, i);
      if (permute(alphabets, startIndex + 1, endIndex)) {
        return true;
      }
      swap(alphabets, i, startIndex);
    }
  }
  return false;
}
function reorder(str) {
  const arr = str.split('').map(c => c.codePointAt(0));
  if (permute(arr)) {
    return arr.map(c => String.fromCodePoint(c)).join('');
  }
  return null;
}

console.log(reorder('аабсд')); // абасд
console.log(reorder('ааабс')); // асаба
console.log(reorder('аааас')); // null