Palindrome or String Manipulation | Dataford Interview Questions

The NatWest mobile app receives customer reference strings that may contain spaces, punctuation, and mixed casing. Write a function that determines whether the reference reads identically forwards and backwards after ignoring non-alphanumeric characters and letter casing.

Formal Specification

Implement is_palindrome(reference), where reference is a string. Return True if the normalized string is a palindrome, otherwise return False. Normalization removes every character that is not alphanumeric and compares letters without regard to case. The original string must not be modified.

Use a two-pointer approach that compares characters from the beginning and end while moving towards the center.

Constraints

0 <= len(reference) <= 200,000
The input contains Unicode characters supported by Python string methods
Only alphanumeric characters are compared
An empty or fully non-alphanumeric string is considered a palindrome

Function Signature

def is_palindrome(reference):

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