2863. Maximum Length of Semi-Decreasing Subarrays

First, solve the problem assuming nums contains distinct values.

Make a new array with each element being the pair (nums[i], i) for every i and call it num_ind.

Sort num_ind in decreasing order.

Iterate over num_ind and store a variable that represents the minimum index (i.e. min of num_ind[i].second) that has been iterated until now. Call it min_index

Now if you are currently on pair (nums[x], x), then ans = max(ans, min_index - x).

Now try to remove the first assumption.