Problem Statement

You are given a palindrome (a string that reads the same forwards and backwards, like "mom"). You must change exactly one character in the string to a lowercase letter from 'a' to 'z' so that: The new string is not a palindrome. The new string is alphabetically smaller than the original string. Among all such possible strings, it is the smallest in alphabetical order. Return this new string. If it is not possible to make such a change, return "IMPOSSIBLE". Example 1 Suppose palindromeStr = "aaabbaaa" Output: "aaaabaaa" Explanation: Possible strings lower alphabetically than "aaabbaaa" after one change are ["aaaabaaa", "aaabaaaa"]. "aaaabaaa" is not a palindrome and is the lowest string that can be created from palindromeStr. Example 2 Suppose palindromeStr = "aaa" Output: "IMPOSSIBLE" Explanation: It is not possible to create an alphabetically lower non-palindromic string. Constraints 1 ≤ length of palindromeStr ≤ 1000 palindromeStr is a palindrome. palindromeStr contains only lo