LeetCode(61)-Valid Palindrome

题目：

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.

思路：

• 题意：判断一个字符串是不是回文
• 这道题可以采用双指针，开头first，结尾sed，first++，sed–，first < sed
• 要求不考虑大小写，全部转化为大写，同时判断字符是不是字母和数字，‘A’，‘Z’，‘0’，‘9’

代码：

public class Solution {    public boolean isPalindrome(String s) {        if(s == null){            return true;        }        char A = 'A';        char Z = 'Z';        char numMin = '0';        char numMax = '9';        s = s.toUpperCase();        int first  = 0;        int sed = s.length() - 1;        while(first < sed){            if((s.charAt(first) < A||s.charAt(first) > Z) && (s.charAt(first) < numMin||s.charAt(first) > numMax)){                first++;                continue;            }            if((s.charAt(sed) < A||s.charAt(sed) > Z) && (s.charAt(sed) < numMin||s.charAt(sed) > numMax)){                sed--;                continue;            }            if(s.charAt(first) == s.charAt(sed)){                first++;                sed--;            }else{                return false;            }        }        return true;    }}