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Grokking the Coding Interview Patterns in C++

Solution: Next Palindrome Using Same Digits

Discover how to efficiently find the next smallest palindrome larger than a given numeric string by applying the two pointers technique. This lesson teaches you to rearrange digits using lexicographical permutations of the left half and mirror it to form the palindrome. You will learn to handle even and odd length palindromes while optimizing time and space complexity.

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Statement

Given a numeric string, numStr, 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 numStr 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:

  • ...