Algorithms & Strings

Python Longest Palindromic Substring

Find the longest contiguous palindromic substring in a given string using the Expand Around Center technique.

Python Source Code

Editable code sample with line numbers

Python

Expected Output

When this program is compiled and executed, the terminal outputs:

'babad' => Longest Palindrome: 'bab'
'cbbd' => Longest Palindrome: 'bb'
'racecar' => Longest Palindrome: 'racecar'
'zencompiler' => Longest Palindrome: 'z'

How the Code Works

There are 2n - 1 possible centers for a palindrome (n single-character centers for odd lengths and n-1 between-character centers for even lengths). Expanding outwards from each center runs in O(N^2) time and O(1) space.

Time Complexity

O(N^2)

Space Complexity

O(1)

Key Takeaways & Best Practices

Expanding around centers handles both odd and even length palindromes without auxiliary memory.
String slicing in Python provides fast substring extraction.

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