[Leetcode] Valid Palindrome

class Solution {public:    bool isPalindrome(string s) {        int start=0;        int end=s.size()-1;        std::transform(s.begin(),s.end(),s.begin(),::tolower);                while(start<end){            while(start<end&&!isAlph(s[start])) start++;            while(start<end&&!isAlph(s[end])) end--;            if(s[start]==s[end]){start++;end--;}            else if(s[start]!=s[end]) return false;        }                if(start>=end)            return true;        else            return false;                }        bool isAlph(char c){            if(c>='a'&&c<='z') return true;            if(c>='0'&&c<='9') return true;        }};