Last Sunday

Level: Beginner 15–30 min

Concepts: Algorithms

Solutions: C# | TypeScript | Python

Write a method that returns the last Sunday of each month for a given year.

Example

last_sunday(2013)

Result
2013-01-27
2013-02-24
2013-03-31
2013-04-28
2013-05-26
2013-06-30
2013-07-28
2013-08-25
2013-09-29
2013-10-27
2013-11-24
2013-12-29

Hint

If you input the year 2020, a leap year, is the last Sunday of February 2020-02-23? If you input the year 2032, also a leap year, is the last Sunday February 2032-02-29?

Reference Walkthrough

Reference implementations in C#, TypeScript, and Python live at tddbuddy-reference-katas/last-sunday. The reference exposes the per-month primitive — find(year, month) with month 1-indexed per human convention — because the per-year list from the TDD Buddy prompt is a trivial map over 1..12 once the month-level math is solved. Ten scenarios cover January through December of 2013, leap-year February edges (2020-02-23, 2032-02-29 where the leap day is Sunday), a century non-leap (2100-02-28), and a four-hundred-divisible leap (2000-12-31 where the last day of the year is Sunday). Each implementation constructs the last day of the month from the standard library and walks back zero-to-six days to Sunday using (weekday_delta + 7) % 7, so the zero-step case falls out of the same arithmetic.

  • C# (.NET 8, xUnit, FluentAssertions 6.12.0) — walkthrough — public static DateOnly Find(int year, int month)
  • TypeScript (Node 20, Vitest 1.6, TS 5 strict) — walkthrough — UTC-disciplined Date: constructed via Date.UTC(...), read via getUTCDay() / getUTCDate() so calendar components stay stable across host time zones
  • Python (3.11, pytest) — walkthrough — datetime.date; note Python’s weekday() has Sunday=6 where C# / JavaScript have Sunday=0, so the walk-back arithmetic changes its target integer but keeps the same shape

This kata ships in Agent Full-Bake mode at high gear (F1 tier): the algorithm is small enough to land as one commit per language, with a brief walkthrough noting there are no builders because the date type comes from the standard library and the inputs/outputs are the domain. See the repo’s Gears section for when high gear is the right call.

Solutions

You can find all language solutions here Last Sunday Solutions

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