A Ruby function to get day of week (Gregorian)

day_of_week.rb

def day_of_week(day, month, year)
  # Zeller's Rule - Jan/Feb are Month 13/14 of previous year
  if month < 3
    month += 12
    year -= 1
  end
  k = year % 100
  j = year / 100
  # Zeller's congruence
  h = (day + (13 * (month + 1)) / 5 + k + (k / 4) + (j / 4) - (2 * j)) % 7
  (h + 6) % 7
end

# 0 = Sun, 6 = Sat

puts day_of_week(20, 7, 1969) # Sun
puts day_of_week(5, 1, 2026) # Mon
puts day_of_week(2, 6, 2020) # Tues 
puts day_of_week(1, 1, 2025) # Weds 
puts day_of_week(4, 7, 1776) # Thurs
puts day_of_week(15, 10, 1582) # Fri
puts day_of_week(3, 4, 1993) # Sat