564. Find the Closest Palindrome ¶

Problem

Given a string n representing an integer, return the closest integer (not including itself), which is a palindrome. If there is a tie, return the smaller one.

The closest is defined as the absolute difference minimized between two integers.

Example 1:

Input: n = "123"
Output: "121"

Example 2:

Input: n = "1"
Output: "0"
Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0.

Constraints:

1 <= n.length <= 18
n consists of only digits.
n does not have leading zeros.
n is representing an integer in the range [1, 10¹⁸ - 1].