Leetcode NO.125 Valid Palindrome

本题题目要求如下：

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.
本题思路还算简单，就是从两边向中间遍历，如果不是数字和字母，就跳过，如果是，就比较。。。
代码如下：

class Solution {
public:
bool isPalindrome(string s) {
int left = 0;
int right = s.length() - 1;
while (left < right) {
if (!isalnum(s[left])) {
++left;
}
else if (!isalnum(s[right])) {
--right;
}
else {
if (tolower(s[left]) != tolower(s[right])) {
cout << left << " " << right << endl;
return false;
}
else {
++left;
--right;
}
}
}
return true;
}
};