What is the optimal time complexity of solving Finding the Longest Palindrome in an Array?

The optimized solution achieves a time complexity of O(n) by using sorting, mathematical shortcuts, or hash table lookups.

What is the auxiliary space complexity for Finding the Longest Palindrome in an Array?

The space complexity is O(1) since we only use a minimal/constant amount of extra memory for tracking variables (or auxiliary space if dynamic structures are allocated).

What are the typical edge cases we must handle in Finding the Longest Palindrome in an Array?

Key edge cases include empty collections, negative or large bounds causing integer overflow, arrays with only one element, or inputs where target criteria are not met.

How can we optimize the brute force approach for Finding the Longest Palindrome in an Array?

Brute force methods often inspect all possible combinations. We optimize this by sorting the input list to enable binary search, or tracking processed items in a set to avoid redundant nested loop lookups.

Back to Practice Dashboard

Python BasicsEasy

Finding the Longest Palindrome in an Array

Learn how to solve the 'Finding the Longest Palindrome in an Array' problem. This detailed resource details brute force and optimized approaches.

Mode Selected

Problem Statement

Easy

Write a function longest_palindrome(arr) that takes a list of positive integers and returns the largest number in the array whose digits form a palindrome. A palindromic number reads the same forwards and backwards (e.g., 121, 1331, 7). If no palindromic number exists, return -1.

Constraints

•1 <= len(arr) <= 10^5
•1 <= arr[i] <= 10^9

Examples

Example 1

Input

arr = [12, 121, 33, 456, 1331]

Output

Explanation

Palindromic numbers: 121, 33, 1331. The largest is 1331.

Example 2

Input

arr = [10, 20, 30]

Output

-1

Explanation

None of 10, 20, 30 are palindromes (10 reversed is 01 which is 1, not 10).

Example 3

Input

arr = [7, 11, 22, 123]

Output

Explanation

Palindromic numbers: 7, 11, 22. The largest is 22.

Need a Hint?

Use simple arithmetic operators (like modulo `%`, division `//`), conditional checks, or loops to inspect number properties.

Edge Cases to Watch

Empty list or null input variables
Single item lists/arrays
Extremely large input bounds causing integer or stack overflow

Ready to Solve?

Open the problem in PyRun's browser-based Python editor. Your code runs fully offline — no server required.

Open in Editor