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Grokking the Coding Interview Patterns in Python

Solution: Next Palindrome Using Same Digits

Explore how to find the next smallest palindrome larger than a given numeric palindrome string by rearranging its digits. Learn to use the two pointers technique to modify only the left half of the palindrome, then mirror it. Understand the process to identify positions for swapping digits, reverse parts for the minimal increment, and handle even and odd-length cases.

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Statement

Given a numeric string, num_str, representing a palindromeA palindrome is a number that reads the same backward as it does forward. (composed only of digits). Return the smallest palindrome larger than num_str that can be created by rearranging its digits. If no such palindrome exists, return an empty string "".

Consider the following example to understand the expected output for a given numeric string:

  • input string = "123321"

  • The valid palindromes made from the exact digits are "213312", "231132", "312213", "132231", "321123".

  • We return the palindrome "132231" because it is the smallest palindrome larger than the input string "123321".

Constraints:

  • ...