120. Valid Palindrome

Easy

Topics

Companies

Helpful tools to learn & understand

Visualize LogicActive Simulator

Watch key transitions, pointers, and variables update step-by-step.

Open

Check Solutions

Read clean, documented implementations across multiple patterns.

View Code

Thinkpad (Draw & Note)

Sketch diagrams on an infinite canvas and draft notes directly inline.

Draw

Example 1:

Input: s = "A man, a plan, a canal: Panama"

Output: true

Explanation: After removing non-alphanumeric characters and converting to lowercase, the string becomes "amanaplanacanalpanama", which is a palindrome.

Example 2:

Input: s = "race a car"

Output: false

Explanation: After removing non-alphanumeric characters and converting to lowercase, the string becomes "raceacar", which is not a palindrome.

Example 3:

Input: s = ""

Output: true

Explanation: An empty string is considered a palindrome.

Example 4:

Input: s = "."

Output: true

Explanation: A string with only non-alphanumeric characters is considered a palindrome after processing.

Example 5:

Input: s = "0P"

Output: false

Explanation: After converting to lowercase and removing non-alphanumeric characters, the string becomes "0p", which is not a palindrome.

Constraints:

•
•

Time Complexity

O(n)

Space Complexity

O(1)

120. Valid Palindrome

Visualize LogicActive Simulator

Check Solutions

Thinkpad (Draw & Note)

Example 1:

Example 2:

Example 3:

Example 4:

Example 5:

Constraints:

Algorithm Overview

Topics

Companies