1
var prevPermOpt1 = function (arr) {
2
  const n = arr.length;
3
  let i = n - 1;
4

5
  while (i > 0 && arr[i] >= arr[i - 1]) i--;
6

7
  if (i === 0) return arr;
8

9
  const swapIndex = i - 1;
10
  const swapDigit = arr[swapIndex];
11

12
  let maxIndex = i;
13
  i = n - 1;
14

15
  while (swapIndex < i) {
16
    const currDigit = arr[i];
17

18
    if (currDigit < swapDigit && currDigit >= arr[maxIndex]) maxIndex = i;
19
    i--;
20
  }
21

22
  [arr[maxIndex], arr[swapIndex]] = [arr[swapIndex], arr[maxIndex]];
23

24
  return arr;
25
};