leetcode之Valid Palindrome

原题如下：

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.
这道题的难度不大，关键是要对当前字符是否是字母数字进行判断，这就要求能够掌握字母数字所对应的ASCII表，其中0-9所对应的ASCII为48-57，A-Z所对应的ASCII码为65-90，a-z所对应的ASCII码为97-122，为了简化判断，可以利用tranform（）方法将大写字母转化成小写字母，然后分别从前后两个方向比较即可。

class Solution {
public:
bool isPalindrome(string s) {
if(s.size() <= 1)
return true;
transform(s.begin(),s.end(),s.begin(),::tolower);
int left = 0,right = s.size() - 1;
while(left < right){
while(left < right && (s[left] < 48 || (s[left] > 57 && s[left] < 97) || s[left] > 122) )
left++;
while(right > left && (s[right] < 48 || (s[right] > 57 && s[right] < 97) || s[right] > 122))
right--;
if(s[left] == s[right])
{
left++;
right--;
}
else
return false;
}
return true;
}
};