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.

题解：这道题比较简单。

class Solution {public:    char strLwr(char c)    {        if(c-'A'>=0 && c-'A'<=26)        {            return 'a'+c-'A';        }           return c;     }        bool isAlphanumeric(char c)    {        if(c-'0'>=0 && c-'0'<=9)        {            return true;        }            if (c-'a'>=0 && c-'a'<=26)        {            return true;        }            if (c-'A'>=0 && c-'A' <= 26)        {            return true;        }            return false;    }         bool isPalindrome(string s) {        int len = s.length();        string ss = "";        int i;        for(i=0; i<len; ++i)        {            if(isAlphanumeric(s[i]))            {                ss += strLwr(s[i]);            }            }          string rss(ss.rbegin(), ss.rend());          if (ss == rss)        {            return true;        }            return false;    }};