Leetcode 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.

注意空字符串也是一个回文！由两个指针i,j分别从前和从后移动，比较字符是否相同。

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