Day 38 LeetCode 125 Valid Palindrome.cpp

/*
125. Valid Palindrome
Solved
Easy

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing
all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
Given a string s, return true if it is a palindrome, or false otherwise.


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.

Example 3:
Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.
 

Constraints:
1 <= s.length <= 2 * 105
s consists only of printable ASCII characters.

*/

class Solution {
public:
    bool isPalindrome(string s) {
        int i = 0, j = s.length() - 1;
        while (i < j) {
            while (i < j && !isalnum(s[i])) i++;
            while (i < j && !isalnum(s[j])) j--;
            if (tolower(s[i]) != tolower(s[j]))
                return false;
            i++;
            j--;
        }
        return true;
    }
};