K-Length Reversed Substrings

Given a string and an integer k, generate all unique substrings of length k and return them in reversed order. If k is greater than the length of the string, return an empty list. Input Format: A string followed by an integer k on the next line. Output Format: A space-separated string containing the unique reversed substrings of length k, or an empty string if no such substrings exist. Example: Input: hello 3 Output: oll ehh Explanation: The unique substrings of length 3 are 'hel', 'ell', 'llo'. Reversing them gives 'leh', 'lle', 'oll'. Unique values combined and sorted to give 'oll ehh'.