【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.

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) {
        int len=s.size();
        int start=0;
        int end=len-1;

        while(start<=end)
        {
            while(start<=end&&!isalnum(s[start]))
                start++;
            while(start<=end&&!isalnum(s[end]))
                end--;

            if(start>end) break;

            if(isdigit(s[start])&&s[start]!=s[end]) return false;

            if(tolower(s[start])!=tolower(s[end])) return false;

            start++;
            end--;
        }

        return true;

    }
};