LeetCode-Valid Palindrome

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Description：
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

题意：判断一个字符串是否是回文，忽略除字母外的其他字符，并且对大小写不敏感；

解法：可以从字符串的首尾处开始向中间遍历，找到出现的字母或者数字，判断两个字符是否相等；

Java

class Solution {
    public boolean isPalindrome(String s) {
        int st = 0;
        int ed = s.length() - 1;
        s = s.toLowerCase();
        while (st < ed) {
            while (st < s.length() && !Character.isLetterOrDigit(s.charAt(st))) st++;
            while (ed >= 0 && !Character.isLetterOrDigit(s.charAt(ed))) ed--;
            if (st >= ed) break;
            if (s.charAt(st) != s.charAt(ed)) return false;
            st++;
            ed--;
        }
        return true;
    }
}