Add gigasecond exercise (#125)

config.json

@@ -315,6 +315,16 @@
         "difficulty": 5,
         "topics": null
       },
+      {
+        "slug": "gigasecond",
+        "name": "Gigasecond",
+        "uuid": "3e8e9e3d-0999-4406-a46d-2a8e2cdfed45",
+        "practices": [],
+        "prerequisites": [
+          "numbers"
+        ],
+        "difficulty": 3
+      },
       {
         "slug": "flatten-array",
         "name": "Flatten Array",

exercises/practice/gigasecond/.docs/instructions.md

@@ -0,0 +1,8 @@
+# Instructions
+
+Your task is to determine the date and time one gigasecond after a certain date.
+
+A gigasecond is one thousand million seconds.
+That is a one with nine zeros after it.
+
+If you were born on _January 24th, 2015 at 22:00 (10:00:00pm)_, then you would be a gigasecond old on _October 2nd, 2046 at 23:46:40 (11:46:40pm)_.

exercises/practice/gigasecond/.docs/introduction.md

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+# Introduction
+
+The way we measure time is kind of messy.
+We have 60 seconds in a minute, and 60 minutes in an hour.
+This comes from ancient Babylon, where they used 60 as the basis for their number system.
+We have 24 hours in a day, 7 days in a week, and how many days in a month?
+Well, for days in a month it depends not only on which month it is, but also on what type of calendar is used in the country you live in.
+
+What if, instead, we only use seconds to express time intervals?
+Then we can use metric system prefixes for writing large numbers of seconds in more easily comprehensible quantities.
+
+- A food recipe might explain that you need to let the brownies cook in the oven for two kiloseconds (that's two thousand seconds).
+- Perhaps you and your family would travel to somewhere exotic for two megaseconds (that's two million seconds).
+- And if you and your spouse were married for _a thousand million_ seconds, you would celebrate your one gigasecond anniversary.
+
+~~~~exercism/note
+If we ever colonize Mars or some other planet, measuring time is going to get even messier.
+If someone says "year" do they mean a year on Earth or a year on Mars?
+
+The idea for this exercise came from the science fiction novel ["A Deepness in the Sky"][vinge-novel] by author Vernor Vinge.
+In it the author uses the metric system as the basis for time measurements.
+
+[vinge-novel]: https://www.tor.com/2017/08/03/science-fiction-with-something-for-everyone-a-deepness-in-the-sky-by-vernor-vinge/
+~~~~

exercises/practice/gigasecond/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/gigasecond.cljs"
+    ],
+    "test": [
+      "test/gigasecond_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "blurb": "Given a moment, determine the moment that would be after a gigasecond has passed.",
+  "source": "Chapter 9 in Chris Pine's online Learn to Program tutorial.",
+  "source_url": "https://pine.fm/LearnToProgram/?Chapter=09"
+}

exercises/practice/gigasecond/.meta/src/example.cljs

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+(ns gigasecond)
+
+;; Given a moment, compute the moment that would be after an arbitrary number
+;; of seconds has passed (one Gigasecond for this example).
+;;
+;; This function works is extreme cases like:
+;; * Periods of any size (any positive number of seconds)
+;; * Periods that include years like 1900 inside (oddly not leap year)
+;; * Periods that start (or end), before (or after), the end of February in
+;;   years that are (or not) leap years
+;; * Periods that start (or end), before (or after), the start (or end) of any
+;;   year
+;;
+;; Note: The number of seconds is embedded as `total-seconds` binding
+(defn from [y m d]
+  ;; Steps:
+  ;; 1) Convert time period to days
+  ;; 2) Compute result thru 3 sections of the period (Start, Middle, End)
+  ;;  2a) Start: Remaining days in first month of the period
+  ;;  2b) Middle: Find last month of the period (loop through months/years)
+  ;;  2c) End: Days in the last month of the period
+  (letfn [;; Helper to compute boolean whether a year is leap or not
+          (leap-year? [year]
+            (cond
+              (zero? (mod year 400)) true
+              (zero? (mod year 100)) false
+              :else (zero? (mod year 4))))
+
+          ;; Helper to compute total number of days in a year's month
+          (days-in-month [year month]
+            (cond
+              (= month 2) (if (leap-year? year) 29 28) ; February
+              (some #(= month %) [4 6 9 11]) 30 ; Abril, June, ...
+              :else 31)) ; January, March, ...
+
+          ;; Helper to compute the number of remaining days of a date's month
+          ;; Ex.: [2000 2 27] results in 3 days because 2000 is a leap year
+          ;;      so day 27, day 28 and day 29 are 3 days in total.
+          ;; (To obtain the total days of a particular month, set day to 1)
+          (days-to-next-month [year month day]
+            (+ (days-in-month year month) (- day) 1))]
+
+    (let [total-seconds 1e9 ;; Gigasecond (works with any positive number)
+          seconds-per-day 86400 ;; 24 x 60 x 60
+          ;; Convert seconds to days
+          total-days (int (/ total-seconds seconds-per-day))]
+
+      ;; Loop thru months decrementing the the total days remaining in period
+      (loop [;; Initialize date and total days in period
+             year y
+             month m
+             day d
+             remaining total-days]
+        (let [;; Compute amount to jump according to distance to next month
+              ;; First loop cycle computes from date's day (step 2a)
+              ;; Following cycles compute from 1st of current month (step 2b)
+              jump (days-to-next-month year month day)]
+          ;; Out of the loop when no more room for another month
+          (if-not (>= remaining jump)
+            ;; Result (step 2c)
+            [year month (+ day remaining)]
+            ;; Update to next month and increment year when necesary
+            (recur ;; Increment year when December jumps to January
+             (if (zero? (mod month 12)) (inc year) year)
+                   ;; Circular month increment (December jumps to January)
+             (inc (mod month 12))
+             1 ;; 1st of month
+                   ;; Decrement the the total days remaining in period
+             (- remaining jump))))))))

exercises/practice/gigasecond/.meta/tests.toml

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+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in a "comment" key.
+
+[92fbe71c-ea52-4fac-bd77-be38023cacf7]
+description = "date only specification of time"
+
+[6d86dd16-6f7a-47be-9e58-bb9fb2ae1433]
+description = "second test for date only specification of time"
+
+[77eb8502-2bca-4d92-89d9-7b39ace28dd5]
+description = "third test for date only specification of time"
+
+[c9d89a7d-06f8-4e28-a305-64f1b2abc693]
+description = "full time specified"
+
+[09d4e30e-728a-4b52-9005-be44a58d9eba]
+description = "full time with day roll-over"

exercises/practice/gigasecond/deps.edn

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+{:deps
+ {org.clojure/clojure {:mvn/version "1.10.1"}
+  org.clojure/clojurescript {:mvn/version "1.10.773"}}
+
+ :aliases
+ {:test
+  {:extra-paths ["test"]
+   :extra-deps
+   {olical/cljs-test-runner {:mvn/version "3.8.0"}}
+   :main-opts ["-m" "cljs-test-runner.main"]}}}

exercises/practice/gigasecond/src/gigasecond.cljs

@@ -0,0 +1,5 @@
+(ns gigasecond)
+
+(defn from []  ;; <- arglist goes here
+    ;; your code goes here
+)

exercises/practice/gigasecond/test/gigasecond_test.cljs

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+(ns gigasecond-test
+  (:require [clojure.test :refer [deftest is]]
+            gigasecond))
+
+(deftest from-apr-25-2011
+  (is (= [2043 1 1] (gigasecond/from 2011 4 25))))
+
+(deftest from-jun-13-1977
+  (is (= [2009 2 19] (gigasecond/from 1977 6 13))))
+
+(deftest from-jul-19-1959
+  (is (= [1991 3 27] (gigasecond/from 1959 7 19))))
+
+;; customize this to test your birthday and find your gigasecond date:
+;; (deftest your-birthday
+;;   (is (= [year2 month2 day2] (gigasecond/from year1 month1 day1))))