Algorithm

We want to rearrange the array to form the next greater permutation. If that's not possible (i.e., it's the last permutation), we return the smallest one (i.e., sorted ascendingly).

To find this next permutation with minimal change, we need to find a digit that can be increased slightly to make the number bigger and then rearrange the remaining part to be the smallest possible.

Traverse from the end and find the first index where the current digit is smaller than the next one (this is the "breaking point").
Then again traverse from the end to find the first digit greater than the breaking point digit and swap them.
Finally, reverse the part of the array to the right of the breaking point to get the smallest next permutation.
If no such breaking point exists (entire array is descending), just reverse the whole array.