🎢 ELI5 Park / Two Pointers / Valid Palindrome
Easy

Valid Palindrome

👶 The 5-Year-Old Summary

Does "racecar" read the same forwards and backwards? Ignore spaces and punctuation! "A man, a plan, a canal: Panama" is a palindrome!

🎮 Interactive Visualizer

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

🧠 The Brain Hack

Two pointers! One at start, one at end. Move toward center, skipping non-alphanumeric. Compare characters at each step!

💻 The Clean Solution

def is_palindrome(s):
    # Clean string: keep only alphanumeric, lowercase
    clean = ''.join(c.lower() for c in s if c.isalnum())
    
    # Two pointers
    left, right = 0, len(clean) - 1
    
    while left < right:
        if clean[left] != clean[right]:
            return False
        left += 1
        right -= 1
    
    return True

# "A man, a plan, a canal: Panama" → True

Time: O(n)

Space: O(n) for clean string