Leetcode 125. 验证回文串

class Solution {
public:
    bool isPalindrome(string s) {
        int l=0,r=(int)s.size()-1;
        while(l<r){
            if(!isalnum(s[l])) ++l;
            else if(!isalnum(s[r])) --r;
            else if(tolower(s[l])==tolower(s[r])) ++l,--r;
            else return false;
        }
        return true;
    }
};