#0182

Longest Palindromic Substring

MediumDSA25 min20 XP

Problem

Given a string, return one longest palindromic substring.

Why This Matters

This problem teaches that two-pointer expansion can replace many repeated substring checks.

Function Signature

def longest_palindrome(s):

Examples

Example 1

Input"babad"

Output"bab" or "aba"

Both bab and aba are valid longest palindromes of length 3.

Constraints

Return the exact requested result.
Handle common edge cases.
Keep the solution readable before optimizing.

CodePython

def longest_palindrome(s):
    """
    Input example: "babad"
    Return: "bab" or "aba"
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return ""

def longest_palindrome(s):
    """
    Input example: "babad"
    Return: "bab" or "aba"
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return ""

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Input"babad"

Expected"bab" or "aba"

Both bab and aba are valid longest palindromes of length 3.

Hidden Test Categories

minimal inputrepeated valueslarger realistic input