125. Valid Palindrome.cpp

#include<iostream>
#include<vector>

using namespace std;


// 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;
            int j = s.length()-1;

            while(i<j){

                if(!isalnum(s[i])){
                    i++;
                    continue;
                }
                if(!isalnum(s[j])){
                    j--;
                    continue;
                }

                if(tolower(s[i]) != tolower(s[j])){
                    return false;
                }

                i++;
                j--;

            }
            
            return true;
        }
};

int main(){

    Solution solution;
    string input = "A man, a plan, a canal: Panama";
    bool answer = solution.isPalindrome(input);
    cout << "Answr is: " << answer << endl;

}