leetcode - Valid Palindrome

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 isAlphanumeric(const char a){
        if( (a >= 'a' && a <= 'z') || (a >= 'A' && a <= 'Z') || (a >= '0' && a <= '9' ))
        return true;
        else
        return false;
    }
    bool isPalindrome(string s) {
        if(s.size()==0) return true;
        string::iterator it_beg = s.begin();
        string::iterator it_end = s.end();
        //bool flag = true;
        //while(!isAlphanumeric(*it_beg) && it_end!=s.end()) it_beg++;
        //while(!isAlphanumeric(*it_end) && it_end!=s.begin()) it_end--;
        while(it_beg < it_end){
            if(!isAlphanumeric(*it_beg)) it_beg++;
            else if(!isAlphanumeric(*it_end)) it_end--;
            else if(*it_beg == *it_end || (*it_beg -*it_end == 'a' - 'A') || (*it_beg -*it_end == 'A' - 'a') ){
                it_beg++;
                it_end--;
            }
            else{
                return false;
            }
        }
        return true;
    }
};