题目描述

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

算法思路

1)将输入的字符串去除标点符号，全部转化为小写
2）设置首尾指针，其中元素相等则首指针+1，尾指针-1,
3）如果最终首指针>=尾指针则是回文，否则就不是

算法实现

class Solution():
    #转化函数
    def toList(self,string):
        string=string.lower()
        string=string.replace(",","").replace(" ","").replace(":","")
        return list(string)
    #是否为回文
    def isValidPalindrome(self,string):
        strList=self.toList(string)
        left=0
        right=len(strList)-1
        while left<right:
            if strList[left]==strList[right]:
                left+=1
                right-=1
            else:
                break
        return left>=right
    
test=Solution()
print(test.isValidPalindrome("A man, a plan, a canal: Panama"))
print(test.isValidPalindrome("race a car"))

小结

判断是否回文的通用方法是首尾双指针
判断最长回文的思路主要是两个字"扩展”