[LeetCode 解题报告]125. Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

class Solution {
public:
    bool isPalindrome(string s) {
        int left = 0, right = s.size() - 1;
        while (left < right) {
            if (!isAlphaNum(s[left]))
                left ++;
            else if (!isAlphaNum(s[right]))
                right --;
            else if ((s[left] + 32 - 'a') % 32 != (s[right] + 32 - 'a') % 32)
                return false;
            else {
                ++left, --right;
            }
        }
        return true;
    }
    
    bool isAlphaNum(char &ch) {
        if (ch >= 'a' && ch <= 'z')
            return true;
        if (ch >= 'A' && ch <= 'Z')
            return true;
        if (ch >= '0' && ch <= '9')
            return true;
        return false;
    }
};