reverse string

reverse the string

def isPalindrome(self, s: str) -> bool:
 
	ans = ""
 
	for c in s:
		if c.isalnum():
			ans += c.lower()
	
	return ans == ans[::-1]

• easy
• time complexity O(n)

using 2 pointers

my solution

def isPalindrome(self, s: str) -> bool:
 
	start = 0
	back = len(s) - 1
 
	while (start < back):
		if not s[start].isalnum():
			start += 1
			continue
		if not s[back].isalnum():
			back -= 1
			continue
		
		if s[start].lower() != s[back].lower():
			return False
 
		start += 1
		back -= 1
 
	return True    

• time: O(n) since we go thru the entire array
• memory: O(1) since we dont use extra memory
• https://www.youtube.com/watch?v=jJXJ16kPFWg
  • neetcode made a separate isalnum() function using ord

def alphanum(self, c):
	return (
		ord('A') <= ord(c) <= ord('Z') or
		ord('a') <= ord(c) <= ord('z') or
		ord('0') <= ord(c) <= ord('9') or
	)