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Every month, your partner meets up with their best friend. Both of them have very busy schedules, making it challenging to find a suitable date! Given your own busy schedule, your partner always double-checks potential meetup dates with you:
In this month's call, your partner asked you this question:
Confused, you ask what a "teenth" day is. Your partner explains that a teenth day, a concept they made up, refers to the days in a month that end in '-teenth':
As there are also seven weekdays, it is guaranteed that each day of the week has exactly one teenth day each month.
Now that you understand the concept of a teenth day, you check your calendar. You don't have anything planned on the teenth Thursday, so you happily confirm the date with your partner.
Your task is to find the exact date of a meetup, given a month, year, weekday and week.
There are five week values to consider: first, second, third, fourth, last, teenth.
For example, you might be asked to find the date for the meetup on the first Monday in January 2018 (January 1, 2018).
Similarly, you might be asked to find:
The teenth week refers to the seven days in a month that end in '-teenth' (13th, 14th, 15th, 16th, 17th, 18th and 19th).
If asked to find the teenth Saturday of August, 1953, we check its calendar:
August 1953
Su Mo Tu We Th Fr Sa
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31
From this we find that the teenth Saturday is August 15, 1953.
Prolog's built-in support for dates is fairly rudimentary. A much nicer way to work with dates is via the [date_time package][date_time-package].
If your installed Swipl version is fairly up-to-date, you can install the package by running:
swipl pack install date_time
If that doesn't work, you can run:
swipl -g 'pack_install(date_time)'
If you're using the online editor, you don't need to manually install anything.
Ad the following code to the top of your solution file to use the date_time package:
:- use_module(library(date_time)).
Tip: the [source of the date_time package][https://www.swi-prolog.org/pack/file_details/date_time/prolog/date_time.pl?show=src] is well documented and be a great help!
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