Two Pointers Cheat Sheet

What is Two Pointers?

Learn to solve problems efficiently using the two-pointer technique.

Template Code

def isPalindrome(s: str) -> bool:
    left, right = 0, len(s) - 1
    
    while left < right:
        # Skip non-alphanumeric from left
        while left < right and not s[left].isalnum():
            left += 1
        # Skip non-alphanumeric from right
        while left < right and not s[right].isalnum():
            right -= 1
        
        # Compare characters (case-insensitive)
        if s[left].lower() != s[right].lower():
            return False
        
        left += 1
        right -= 1
    
    return True

Complexity

Common Variations

• Basic Two Pointers
• Two Pointers with constraints
• Optimized Two Pointers

Practice Problems