LeetCode: Valid Palindrome II

Posted on February 17, 2018July 26, 2020 by braindenny

Valid Palindrome II

Similar Problems:

Given a non-empty string s, you may delete at most one character. Judge whether you can make it a palindrome.

Example 1:
Input: "aba"
Output: True

Example 2:
Input: "abca"
Output: True
Explanation: You could delete the character 'c'.

Note:
The string will only contain lowercase characters a-z. The maximum length of the string is 50000.

Github: code.dennyzhang.com

Credits To: leetcode.com

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

## https://code.dennyzhang.com/valid-palindrome-ii
## Basic Ideas: If mismatched, we can only delete either the left or the right
##
## Complexity: Time O(n), Space O(1)
class Solution(object):
    def validPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        if self.isPalindrome(s): return True
        l, r = 0, len(s)-1
        while l<r:
            if s[l]!=s[r]:
                # keep right
                if self.isPalindrome(s[l+1:r+1]): return True
                # keep left
                if self.isPalindrome(s[l:r]): return True
                return False
            l,r = l+1, r-1
        return True

    def isPalindrome(self, s):
        length = len(s)
        if length == 0: return True
        l, r = 0, length-1
        while l<r:
            if s[l]!=s[r]: return False
            l, r = l+1, r-1
        return True

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