A leap year happens every four years, so it's a year that is perfectly divisible by four. However, if the year is a multiple of 100 (1800, 1900, etc), the year must be divisible by 400.
Write a function that determines if the year is a leap year or not.
leap_year(2020) ➞ True
leap_year(2021) ➞ False
leap_year(1968) ➞ TrueN/A