LeetCode——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.

解答：

class Solution {public:    bool isAlphanumeric(char c) {        if (c >= 'a' && c <= 'z') {            return true;        }        if (c >= 'A' && c <= 'Z') {            return true;        }        if (c >= '0' && c <= '9') {            return true;        }        return false;    }    bool isAlphanumericEqual(char a, char b) {        if (a == b) {            return true;        }        if ((a < '0' || a > '9') && (b < '0' || b > '9'))         {            //两个不同字母            if (a > b) {                a = a - 'a';                b = b - 'A';            } else {                a = a - 'A';                b = b - 'a';            }            return a == b;        }        return false;    }    bool isPalindrome(string str) {        if (str.length() == 0) return true;        int s = 0;        int e = str.length() - 1;        while (s < e) {            while (s < e && !isAlphanumeric(str[s])) ++s;            if (s >= e) {                return true;            }            while (s < e && !isAlphanumeric(str[e])) --e;            if (s >= e) {                return true;            }            if (!isAlphanumericEqual(str[s], str[e])) {                return false;            }            ++s;            --e;        }        return true;    }};