125. Valid Palindrome.cpp

// 125. Valid Palindrome
// Solved
// Easy
// Topics
// Companies
// 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 start=0;
       int end=s.size()-1;
       while(start<=end){
           if(!isalnum(s[start])){
            start++;
            continue;
            }
           if(!isalnum(s[end])){
            end--;
            continue;
            }
           if(tolower(s[start])!=tolower(s[end]))
           return false;
           else{
               start++;
               end--;
           }
       }
       return true;
}
};