How do I practice coding and algorithm questions?

Use PracHub's coding console to write, test, and debug your solutions in Python or JavaScript. View hints, test against sample inputs, and compare with official solutions.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Uber during technical interviews.

Find the Next Larger Palindrome | Uber Coding Question

Find the Next Larger Palindrome

Company: Uber

Role: Data Scientist

Category: Coding & Algorithms

Interview Round: Onsite

Given a positive integer `n`, return the smallest integer strictly greater than `n` whose decimal representation is a palindrome. A palindrome reads the same from left to right and right to left. Do not allow leading zeros. Examples: - `n = 9` -> `11` - `n = 123` -> `131` - `n = 808` -> `818` - `n = 999` -> `1001` Discuss edge cases such as single-digit inputs, numbers consisting only of `9`s, even versus odd digit lengths, and inputs that are already palindromes.

Quick Answer: This question evaluates proficiency in numeric and string manipulation, algorithmic thinking, and edge-case reasoning related to palindromic number generation.

Given a positive integer `n`, return the smallest integer strictly greater than `n` whose decimal representation is a palindrome. A palindrome reads the same from left to right and right to left. The result must not contain leading zeros. Examples: - `9 -> 11` - `123 -> 131` - `808 -> 818` - `999 -> 1001` Be careful with edge cases such as single-digit inputs, numbers made entirely of `9`s, even versus odd digit lengths, and inputs that are already palindromes. A brute-force approach that checks every number after `n` is not efficient enough; instead, reason about how palindromes are formed.

Constraints

1 <= n < 10^18
The returned palindrome must have no leading zeros

Examples

Input: (1,)

Expected Output: 2

Explanation: The next integer after 1 is 2, and every single-digit number is a palindrome.

Input: (9,)

Expected Output: 11

Explanation: After 9, the next palindrome is 11.

Input: (123,)

Expected Output: 131

Explanation: Mirroring gives 121, which is too small, so the middle is increased to produce 131.

Input: (808,)

Expected Output: 818

Explanation: 808 is already a palindrome, but the answer must be strictly larger, so the next one is 818.

Input: (1221,)

Expected Output: 1331

Explanation: 1221 is a palindrome with even length. The next larger palindrome is obtained by increasing the middle pair.

Input: (12932,)

Expected Output: 13031

Explanation: Mirroring gives 12921, which is too small. Incrementing the middle with carry leads to 13031.

Input: (999,)

Expected Output: 1001

Explanation: For numbers consisting only of 9s, the next palindrome has one more digit: 1001.

Hints

Try building a palindrome by copying the left half of the number onto the right half.
If that mirrored number is not strictly greater than `n`, increment the middle digit(s) and mirror again. Numbers like 9, 99, and 999 need special handling.

Quick Overview

This question evaluates proficiency in numeric and string manipulation, algorithmic thinking, and edge-case reasoning related to palindromic number generation.