Given an array of positive integers
arr (not necessarily distinct), return the lexicographically largest permutation that is smaller than
arr, that can be made with exactly one swap (A swap exchanges the positions of two numbers
arr[j]). If it cannot be done, then return the same array.
Input: arr = [3,2,1] Output: [3,1,2] Explanation: Swapping 2 and 1.
Input: arr = [1,1,5] Output: [1,1,5] Explanation: This is already the smallest permutation.
Input: arr = [1,9,4,6,7] Output: [1,7,4,6,9] Explanation: Swapping 9 and 7.
Input: arr = [3,1,1,3] Output: [1,3,1,3] Explanation: Swapping 1 and 3.
1 <= arr.length <= 104
1 <= arr[i] <= 104