Valid Palindrome

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.

class Solution {public:    bool isPalindrome(string s) {        // Start typing your C/C++ solution below        // DO NOT write int main() function            int n =s.length();int l=0,r=n-1;while(l<=r){while(l<=r&&!isalnum(s[l]))l++;while(l<=r&&!isalnum(s[r]))r--;if ( l> r)break;if (isdigit(s[l]) && s[l]!=s[r] )return false;if ( tolower(s[l])!=tolower(s[r]))return false;l++,r--;}return true;    }};