[LeetCode125] Valid Palindrome

题目：

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.

分类：String Two Pointers

代码：

class Solution {
public:
    bool isPalindrome(string s) {
        string str;
        for (auto c : s)
        {
            if (isalpha(c))
            {
                str += tolower(c);
            }
            else if (isdigit(c))
            {
                str += c;
            }
        }

        
        for(int left = 0, right = str.size() - 1; left < right; ++left, --right)
        {
            if(str[left] != str[right])
                return false;
        }
        return true;
    }
};