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.

丑陋AC代码

class Solution {
public:
    bool isPalindrome(string s){
        if(s.empty())
            return true;
        int start = 0, end = s.size() - 1;
        while(start < end){
            if(!((s[start] >= 'A' && s[start] <= 'Z') || (s[start] >= 'a' && s[start] <= 'z') || (s[start] >= '0' && s[start] <= '9'))){
                start++;
                continue;
            }
            if(!((s[end] >= 'A' && s[end] <= 'Z') || (s[end] >= 'a' && s[end] <= 'z') || (s[end] >= '0' && s[end] <= '9'))){
                end--;
                continue;
            }
            if(!(s[start] == s[end] || ( s[start] - s[end] == 'A' - 'a' || s[end] - s[start] == 'A' - 'a'))){
                return false;
            }
            start++;
            end--;
            
        }
        return true;
    }
};