Palindrome String: Free. No login required. Python technical interview question

Given a string, you need to determine whether it is a palindrome or not.

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward. For example, "racecar" is a palindrome because if you reverse the order of its letters, you still get "racecar". Similarly, "level", "deified", and "A man a plan a canal Panama" are all palindromes.

Write a function that takes a string as input and returns true if the string is a palindrome, or false otherwise.

For the purposes of this problem, you should ignore any non-alphanumeric characters and treat upper-case and lower-case letters as the same character.

- The task is to determine if a given string is a palindrome.
- Ignore non-alphanumeric characters, and treat upper- and lower-case letters as the same.
- The goal is to avoid extra storage, so we'll use character-by-character comparison instead of storing a reversed string.

Understanding the Problem

- Use a two-pointer technique, one starting from the beginning and one from the end of the string.
- Increment the left pointer and decrement the right pointer after each comparison.

Use Two Pointers to Compare Characters

- As you move the two pointers, skip any characters that are not alphanumeric (like spaces, punctuation).
- Use Python's `isalnum()` method to check if a character is alphanumeric.

Skip Non-Alphanumeric Characters

- Compare the characters at the left and right pointers, ignoring case.
- If the characters are not equal, the string is not a palindrome and you can return `False` immediately.

Compare Characters (Ignore Case)

- If all characters match as you move the pointers, the string is a palindrome.
- Once the two pointers meet or cross, return `True` to indicate the string is a palindrome.

Return the Result

- Consider edge cases like an empty string or a string containing only non-alphanumeric characters.
- These should return `True` since they can be considered palindromes.

Interview question: Palindrome String

Example 1

Example 2

Example 3

Example 4

Test

Results