125.valid-palindrome.cpp

/*
 * @lc app=leetcode id=125 lang=cpp
 *
 * [125] Valid Palindrome
 *
 * https://leetcode.com/problems/valid-palindrome/description/
 *
 * algorithms
 * Easy (37.82%)
 * Likes:    1809
 * Dislikes: 3641
 * Total Accepted:    810K
 * Total Submissions: 2.1M
 * Testcase Example:  '"A man, a plan, a canal: Panama"'
 *
 * Given a string s, determine if it is a palindrome, considering only
 * alphanumeric characters and ignoring cases.
 * 
 * 
 * Example 1:
 * 
 * 
 * Input: s = "A man, a plan, a canal: Panama"
 * Output: true
 * Explanation: "amanaplanacanalpanama" is a palindrome.
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: s = "race a car"
 * Output: false
 * Explanation: "raceacar" is not a palindrome.
 * 
 * 
 * 
 * Constraints:
 * 
 * 
 * 1 <= s.length <= 2 * 10^5
 * s consists only of printable ASCII characters.
 * 
 * 
 */

// @lc code=start
class Solution {
public:
    bool isPalindrome(string s) {
        int left = 0, right = s.length() - 1;
        while (left < right) {
            while (left < right && !isalnum(s[left]))
                ++left;
            while (left < right && !isalnum(s[right]))
                --right;
            if (left >= right)
                break;
            if (tolower(s[left]) != tolower(s[right]))
                return false;
            ++left, --right;
        }
        return true;
    }
};
// @lc code=end