125.验证回文串.py

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# @lc app=leetcode.cn id=125 lang=python3
#
# [125] 验证回文串
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# https://leetcode-cn.com/problems/valid-palindrome/description/
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# algorithms
# Easy (42.34%)
# Likes:    154
# Dislikes: 0
# Total Accepted:    77.6K
# Total Submissions: 183.3K
# Testcase Example:  '"A man, a plan, a canal: Panama"'
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# 给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。
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# 说明：本题中，我们将空字符串定义为有效的回文串。
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# 示例 1:
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# 输入: "A man, a plan, a canal: Panama"
# 输出: true
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# 示例 2:
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# 输入: "race a car"
# 输出: false
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# 
#

# @lc code=start
class Solution:
    def isPalindrome(self, s: str) -> bool:
        # 双指针
        l, r = 0, len(s) - 1
        while l < r:
            while l < r and not s[l].isalnum():
                l += 1
            while l < r and not s[r].isalnum():
                r -= 1
            if s[l].lower() != s[r].lower():
                return False
            l += 1
            r -= 1
        return True


        
# @lc code=end