# Leetcode: Valid Palindrome

Valid Palindrome

Similar Problems:

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

```Input: "A man, a plan, a canal: Panama"
Output: true
```

Example 2:

```Input: "race a car"
Output: false
```

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/valid-palindrome
## Basic Ideas: two pointer
##
## Complexity: Time O(n), Space O(1)
class Solution(object):
def isPalindrome(self, s):
"""
:type s: str
:rtype: bool
"""
length = len(s)
if length == 0: return True
left, right = 0, length-1
while left<right:
if not s[left].isalnum():
left += 1
continue
if not s[right].isalnum():
right -= 1
continue
if s[left].lower() != s[right].lower():
return False
left, right = left+1, right-1
return True
```

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