125. Valid Palindrome

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.

def remove_non_alphanumeric(input_str):
    result_str = ''.join(char for char in input_str if char.isalnum())
    return result_str

def remove_non_alphanumeric(input_str): 
	result_str = "" 
	for char in input_str: 
		if char.isalnum(): 
			result_str += char 
	return result_str