LeetCode 125 Valid Palindrome

最新推荐文章于 2020-05-27 12:11:01 发布

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本文介绍了一种使用双指针法判断字符串是否为回文的方法，该方法忽略了所有非字母数字字符，并对大小写不敏感。适用于空字符串的情况。

原题:（频率5）

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

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

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

题意：判断是否是合格的回文串，忽略空格和标点符号

代码和思路：

class Solution {
    public boolean isPalindrome(String s) {
        if(s.isEmpty()) return true;
        //双指针法
        int start = 0;
        int end = s.length()-1;
        while(start<=end){
            char cstart = s.charAt(start);
            char cend   = s.charAt(end);
            //首位向中间走，如果不是字母或数字，跳过
            if(!Character.isLetterOrDigit(cstart)) start++;
            else if(!Character.isLetterOrDigit(cend)) end--;
            //是数字或字母的话，判断是否相等，相等的话继续向中间移动
            else{
                if(Character.toLowerCase(cstart)!=Character.toLowerCase(cend)) return false;
                start++;
                end--;
            }
           
        }
        return true;
    }
}