Leetcode[125]-Valid Palindrome

Link: https://leetcode.com/problems/valid-palindrome/

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.

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思路：定义两个标示符，一个指向字符串前面，一个指向字符串末尾，如果前后位置的字符不是字母或是数字，则直接跳过该字符，如果是大写，则转换成小写再比较，如果碰到不匹配的直接返回false。

Code(C++):

class Solution {public:    bool isPalindrome(string s) {        int length = s.length();        if(length == 0){              return true;          }          int i = 0, j = length-1;        while(i <= j){            if(!isStr(s[i])) i++;            else if(!isStr(s[j])) j--;            else if(s[i++] != s[j--]) return false;        }        return true;    }    bool isStr(char &a){        if(a >= '0' && a <= '9' ) {            return true;        }else if(a >= 'a' && a <= 'z' ) {            a -= 32;            return true;        } else if(a >= 'A' && a <= 'Z' ) {            return true;        }         return false;    }};