// https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/no-repeats-please

function permAlone(str) {
  let noRepeatsCount = 0;
  noRepeatsCount += Number(!/(.{1})\1/.test(str));

  function swap(Arr, iA, iB) {
    const tmp = Arr[iA];
    Arr[iA] = Arr[iB];
    Arr[iB] = tmp;
  }

  const strArr = str.split("");
  const strLength = strArr.length;
  // Heap's Algorithm as explained @ https://www.baeldung.com/cs/array-generate-all-permutations
  const c = Array(strLength).fill(0);
  let i = 0;
  while (i < strLength) {
    if (c[i] < i) {
      if (i % 2) {
        swap(strArr, c[i], i);
      } else {
        swap(strArr, 0, i);
      }
      noRepeatsCount += Number(!/(.{1})\1/.test(strArr.join("")));
      c[i]++;
      i = 0;
    } else {
      c[i] = 0;
      i++;
    }
  }

  return noRepeatsCount;
}

console.log(permAlone("abcdefa"));