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#!/bin/python3

# Doomsday algorithm info: https://en.wikipedia.org/wiki/Doomsday_rule

DOOMSDAY_LEAP = [4, 1, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5]

DOOMSDAY_NOT_LEAP = [3, 7, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5]

WEEK_DAY_NAMES = {

0: "Sunday",

1: "Monday",

2: "Tuesday",

3: "Wednesday",

4: "Thursday",

5: "Friday",

6: "Saturday",

}

def get_week_day(year: int, month: int, day: int) -> str:

"""Returns the week-day name out of a given date.

>>> get_week_day(2020, 10, 24)

'Saturday'

>>> get_week_day(2017, 10, 24)

'Tuesday'

>>> get_week_day(2019, 5, 3)

'Friday'

>>> get_week_day(1970, 9, 16)

'Wednesday'

>>> get_week_day(1870, 8, 13)

'Saturday'

>>> get_week_day(2040, 3, 14)

'Wednesday'

"""

# minimal input check:

assert len(str(year)) > 2, "year should be in YYYY format"

assert 1 <= month <= 12, "month should be between 1 to 12"

assert 1 <= day <= 31, "day should be between 1 to 31"

# Doomsday algorithm:

century = year // 100

century_anchor = (5 * (century % 4) + 2) % 7

centurian = year % 100

centurian_m = centurian % 12

dooms_day = (

(centurian // 12) + centurian_m + (centurian_m // 4) + century_anchor

) % 7

day_anchor = (

DOOMSDAY_NOT_LEAP[month - 1]

if (year % 4 != 0) or (centurian == 0 and (year % 400) == 0)

else DOOMSDAY_LEAP[month - 1]

)

week_day = (dooms_day + day - day_anchor) % 7

return WEEK_DAY_NAMES[week_day]

if __name__ == "__main__":

import doctest

doctest.testmod()

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