[New practice exercise] Meetup (#499)

* empty template

* [New practice exercise] Meetup

* sorted config.json

Author: colinleach

config.json

@@ -980,6 +980,14 @@
         "prerequisites": [],
         "difficulty": 4
       },
+      {
+        "slug": "meetup",
+        "name": "Meetup",
+        "uuid": "af65d283-cb78-4bee-b1d1-557d677e775d",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "flower-field",
         "name": "Flower Field",

exercises/practice/meetup/.docs/instructions.md

@@ -0,0 +1,34 @@
+# Instructions
+
+Your task is to find the exact date of a meetup, given a month, year, weekday and week.
+
+There are six 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 third Tuesday of August 2019 (August 20, 2019)
+- the teenth Wednesday of May 2020 (May 13, 2020)
+- the fourth Sunday of July 2021 (July 25, 2021)
+- the last Thursday of November 2022 (November 24, 2022)
+- the teenth Saturday of August 1953 (August 15, 1953)
+
+## Teenth
+
+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:
+
+```plaintext
+    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.

exercises/practice/meetup/.docs/introduction.md

@@ -0,0 +1,29 @@
+# Introduction
+
+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:
+
+- "Can I meet up on the first Friday of next month?"
+- "What about the third Wednesday?"
+- "Maybe the last Sunday?"
+
+In this month's call, your partner asked you this question:
+
+- "I'd like to meet up on the teenth Thursday; is that okay?"
+
+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':
+
+- 13th (thirteenth)
+- 14th (fourteenth)
+- 15th (fifteenth)
+- 16th (sixteenth)
+- 17th (seventeenth)
+- 18th (eighteenth)
+- 19th (nineteenth)
+
+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.

exercises/practice/meetup/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "colinleach"
+  ],
+  "files": {
+    "solution": [
+      "meetup.R"
+    ],
+    "test": [
+      "test_meetup.R"
+    ],
+    "example": [
+      ".meta/example.R"
+    ]
+  },
+  "blurb": "Calculate the date of meetups.",
+  "source": "Jeremy Hinegardner mentioned a Boulder meetup that happens on the Wednesteenth of every month"
+}

exercises/practice/meetup/.meta/example.R

@@ -0,0 +1,28 @@
+library(lubridate)
+library(stringr)
+
+day_abbrevs <- c("Sun" = 1, "Mon" = 2, "Tue" = 3, "Wed" = 4,
+                 "Thu" = 5, "Fri" = 6, "Sat" = 7)
+week_specifiers <- c("first" = 1, "second" = 2, "third" = 3,
+                     "fourth" = 4, "fifth" = 5)
+
+meetup <- function(year, month, week, day_of_week) {
+  curr_month <- make_date(year, month)
+  days <- make_date(year, month, 1:days_in_month(curr_month))
+  num_dow <- day_abbrevs[str_sub(day_of_week, 1, 3)]
+  valid_dates <- days[wday(days) == num_dow]
+
+  if (week %in% names(week_specifiers) &&
+        length(valid_dates) >= week_specifiers[week]) {
+    result <- valid_dates[week_specifiers[week]]
+  } else if (week == "last") {
+    result <- max(valid_dates)
+  } else if (week == "teenth") {
+    teenth <- valid_dates[day(valid_dates) %in% 13:19]
+    result <- teenth
+  } else {
+    stop("Invalid input")
+  }
+
+  result |> as.character()
+}

exercises/practice/meetup/.meta/template.j2

@@ -0,0 +1,16 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+
+{{ macros.header() }}
+
+{% for case in cases -%}
+test_that("{{ case["description"] }}", {
+  year <- {{ case["input"]["year"] }}
+  month <- {{ case["input"]["month"] }}
+  week <- "{{ case["input"]["week"] }}"
+  day_of_week <- "{{ case["input"]["dayofweek"] }}"
+  expected <- "{{ case["expected"] }}"
+  expect_equal({{ case["property"] }}(year, month, week, day_of_week), expected)
+})
+
+{% endfor %}