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

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 isPalindrome(string s) {
        
        int i,j,len;
        len=s.length();
        transform(s.begin(), s.end(), s.begin(), ::toupper);
        for(i=0,j=len-1;i<j;i++,j--)
        {
            while(!(s[i]<='Z'&&s[i]>='A'||s[i]>='0'&&s[i]<='9'))
            {
                i++;
                if(i>=j)
                    return true;
            }
            while(!(s[j]<='Z'&&s[j]>='A'||s[j]>='0'&&s[j]<='9'))
            {
                j--;
                if(i>=j)
                    return true;
            }
            if(s[i]!=s[j])
               return false;
        }
        return true;
    }
};