Is Next Palindrome Using Same Digits easy or hard?

The problem is rated Hard because the key insight is non-obvious. Many candidates initially attempt full permutations, but the correct solution reduces the search space by applying next permutation only to the first half of the palindrome.

Next Palindrome Using Same Digits Python/Java solution

Implement the next permutation algorithm on the first half of the string. Python typically converts the string to a list for swaps and reversal, while Java uses a char array. After computing the next half, mirror it to build the full palindrome.

How to solve Next Palindrome Using Same Digits in O(n)?

Extract the first half of the palindrome and apply the standard next permutation algorithm. After generating the next lexicographically larger arrangement of that half, rebuild the palindrome by mirroring it. If the string length is odd, keep the middle character unchanged and mirror the rest.

What is the best approach for Next Palindrome Using Same Digits?

The optimal approach computes the next permutation of the first half of the palindrome and mirrors it to rebuild the full number. Because a palindrome is determined entirely by its left half, modifying that portion generates the next valid candidate. This method runs in O(n) time and O(n) space.

Is Next Palindrome Using Same Digits asked at Google/Amazon/Meta?

Palindrome permutation and next-permutation style problems appear frequently in interviews at companies like Google, Amazon, and Meta. Variations test understanding of lexicographic permutations, string manipulation, and two-pointer techniques.

What data structure is used in Next Palindrome Using Same Digits?

The solution mainly uses string or character array manipulation. The next-permutation process operates directly on an array of digits with swaps and reversals, while two-pointer comparisons are used conceptually when reasoning about palindrome structure.

What is the time complexity of Next Palindrome Using Same Digits?

The optimal algorithm runs in O(n) time because it scans the first half of the string to perform the next-permutation steps and then constructs the mirrored palindrome. Space complexity is O(n) due to string manipulation and rebuilding the result.

Description Hints 2 Solution Video 25:47

1842. Next Palindrome Using Same Digits

Hard54.2% acceptance1 companyPremium elsewhere, free here

You are given a numeric string num, representing a very large palindrome.

Return the smallest palindrome larger than num that can be created by rearranging its digits. If no such palindrome exists, return an empty string "".

A palindrome is a number that reads the same backward as forward.

Example 1:

Input: num = "1221"
Output: "2112"
Explanation: The next palindrome larger than "1221" is "2112".

Example 2:

Input: num = "32123"
Output: ""
Explanation: No palindromes larger than "32123" can be made by rearranging the digits.

Example 3:

Input: num = "45544554"
Output: "54455445"
Explanation: The next palindrome larger than "45544554" is "54455445".

Constraints:

1 <= num.length <= 10⁵
num is a palindrome.

Asked at 1 company

Amazon

Topics

String Two Pointers

Hints open one at a time

Hint 1

Is it possible to swap one character in the first half of the palindrome to make the next one?

Hint 2

Are there different cases for when the length is odd and even?

25:47

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