2 Pointer Palindrome - codepath/compsci_guides GitHub Wiki

Unit 4 Session 1 (Click for link to problem statements)

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

• What if the string is empty?
  • An empty string is considered a palindrome as it reads the same forward and backward.

P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Use two pointers to compare characters from the beginning and end of the string moving towards the center.

1) Initialize two pointers, left at the start (0) and right at the end (length of s - 1)
2) While left pointer is less than right pointer:
  a) If characters at left and right pointers do not match, return False
  b) Increment left pointer and decrement right pointer
3) If all characters match, return True

⚠️ Common Mistakes

• Not handling strings of different lengths properly.
• Incorrectly initializing the pointers.

I-mplement

def is_palindrome(s):
    left = 0
    right = len(s) - 1
    while left < right:
        if s[left] != s[right]:
            return False
        left += 1
        right -= 1
    return True