Leetcode - 125. Valid Palindrome

 Problem statement:

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.

Solution:

Problem says,

1. First convert all uppercase letters into lowercase letters.
2. Remove all non-alphanumeric characters.

For first part, I will use ToLower() method of string class. this method will convert all the uppercase letters into lowercase letters.

For the second part, I will use Regex Replace method to remove all non-alphanumeric characters.

 public bool IsPalindrome(string s) 

 {

        /*here i am checking if string is null or empty if so then it will be always                                    Palindrome so return true*/

            if(string.IsNullOrEmpty(s))

               return true;

    /*in this statement i am first converting the string all uppercase to lowercase letters and     then replacing all the non-alphanumeric characters with empty means it will remove that*/

        var str=Regex.Replace(s.ToLower(),"[^a-z0-9]","");

             

        int i=0, j=str.Length-1;

        for(;i<j;i++,j--)

            {

               /*in this statement i am comparing the first character to last character if it is not                     same then returning false*/

            if(str[i]!=str[j])

                return false;

        }

       return true;

    }