Problem 43072. Check if a rotated array was originally sorted

Suppose a sorted array is rotated at some pivot unknown to you. For example, [0 1 2 4 5 6 7] might become [5 6 7 0 1 2 4].

Given a rotated array, find out if it was originally sorted. Your function will return true for this array: [4 5 6 7 0 1 2]. But it will return false for [2 5 6 8 0 1 3], because its original array, i.e., [0 1 3 2 5 6 8], was not sorted.