leetcode之Valid Palindrome

class Solution {
public:
    bool isPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (s.empty()) {
            return true;
        }
        string temp;
        for (int i=0; i<s.size(); i++) {
            if (isalnum(s[i])) {
                temp.push_back(toupper(s[i]));
            }
        }
        if (temp.size()<=1) {
            return true;
        }
        int beg = 0;
        int end = temp.size()-1;
        while (beg < end) {
            if (temp[beg] == temp[end]) {
                beg++;
                end--;
            } else {
                return false;
            }
        }
        return true;
    }
};