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.

#include 
     
      #include 
      
       #include 
       
        using std::string;class Solution {    public:        bool isAlphaNumber(char & c)        {            if (c >= '0' && c <= '9')            {                return true;            }            if (c >= 'a' && c <= 'z')            {                return true;            }            if (c >= 'A' && c <= 'Z')            {                c += 'a' - 'A';                return true;            }            return false;        }        bool isPalindrome(string s) {            // Start typing your C/C++ solution below            //         // DO NOT write int main() function            //                             if (s.empty())            {                return true;            }            int i = 0, j = s.size() - 1;            char a,b;            while(i < s.size() && j >= 0){                a = s.at(i);                b = s.at(j);                if (!isAlphaNumber(a))                {                    i++;                    continue;                }                if (!isAlphaNumber(b))                {                    j--;                    continue;                }                if (a == b)                {                    i++;                    j--;                }else                {                    return false;                }            }            //if (i + j != s.size())            //{            //    return false;            //}else            {                return true;            }        }};