Reverse an Array and Duplicate Elements

EasyPython

Problem

Infor OS processes ordered configuration values represented as arrays. Given a mutable integer array nums and an index index, duplicate the element originally stored at index, then reverse the entire resulting array.

The operation must modify nums in place and return the same list object. The duplicated values must remain adjacent after reversal. In other words, first insert a copy immediately after the selected element, then reverse the complete array.

Formal Specification

Implement reverse_and_duplicate(nums, index):

Input: nums, a non-empty list of integers, and index, a valid zero-based index in the original list.
Output: The modified nums list after duplicating nums[index] and reversing the result.
The original relative order should be reversed, except that the selected value appears twice consecutively.
Use O(1) auxiliary space. The input list may grow by one element.

Constraints

1 <= len(nums) <= 10^5
0 <= index < len(nums)
-10^9 <= nums[i] <= 10^9

Function Signature

def reverse_and_duplicate(nums, index):

Formal Specification

Implement reverse_and_duplicate(nums, index):

Input: nums, a non-empty list of integers, and index, a valid zero-based index in the original list.
Output: The modified nums list after duplicating nums[index] and reversing the result.
The original relative order should be reversed, except that the selected value appears twice consecutively.
Use O(1) auxiliary space. The input list may grow by one element.