【leetcode】125. Valid Palindrome【java】

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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.

先将所有字符变为小写，运用两个指针，一个从头开始，一个从尾开始

public class Solution {    public boolean isPalindrome(String s) {        if (s == null) {            return true;        }        s = s.toLowerCase();        int i = 0;        int j = s.length() - 1;        while (i < j) {            if ((s.charAt(i) > 'z' || s.charAt(i) < 'a') && (s.charAt(i) > '9' || s.charAt(i) < '0')) {                i++;            } else if ((s.charAt(j) > 'z' || s.charAt(j) < 'a') && (s.charAt(j) > '9' || s.charAt(j) < '0')) {                j--;            } else if (s.charAt(i++) != s.charAt(j--)){                return false;            }        }        return true;    }}

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