LeetCode 125. Valid Palindrome

好久没写代码了.................

代码：

class Solution {public:    bool isPalindrome(string s)     {    string str(1, '/');    for (size_t i = 0; i < s.size(); ++ i)    {    if (s[i]>='a' && s[i]<='z')    {    str.append(1, s[i]);    str.append(1, '/');        } else if (s[i]>='A' && s[i]<='Z')    {    str.append(1, s[i]-'A'+'a');    str.append(1, '/');    } else if (s[i]>='0' && s[i]<='9')    {    str.append(1, s[i]);    str.append(1, '/');    }    }    int mid = str.size() / 2;    for (int i = 1; mid-i>=0 && mid+i<str.size(); ++ i)    {    if (str[mid-i] != str[mid+i])    {    return false;    }    }    return true;    }};