1842. Next Palindrome Using Same Digits

class Solution:
    def nextPalindrome(self, num: str) -> str:
        def next_permutation(nums: List[str]) -> bool:
            n = len(nums) // 2
            i = n - 2
            while i >= 0 and nums[i] >= nums[i + 1]:
                i -= 1
            if i < 0:
                return False
            j = n - 1
            while j >= 0 and nums[j] <= nums[i]:
                j -= 1
            nums[i], nums[j] = nums[j], nums[i]
            nums[i + 1 : n] = nums[i + 1 : n][::-1]
            return True

        nums = list(num)
        if not next_permutation(nums):
            return ""
        n = len(nums)
        for i in range(n // 2):
            nums[n - i - 1] = nums[i]
        return "".join(nums)