Add pop-count (#293)

config.json

@@ -356,6 +356,14 @@
         "prerequisites": [],
         "difficulty": 1
       },
+      {
+        "slug": "pop-count",
+        "name": "Pop Count",
+        "uuid": "4c32e86e-cd3e-4be9-b581-24144c548751",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "word-count",
         "name": "Word Count",

exercises/practice/pop-count/.docs/instructions.md

@@ -0,0 +1,8 @@
+# Instructions
+
+Your task is to count the number of 1 bits in the binary representation of a number.
+
+## Restrictions
+
+Keep your hands off that bit-count functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/pop-count/.docs/introduction.md

@@ -0,0 +1,47 @@
+# Introduction
+
+Your friend Eliud inherited a farm from her grandma Tigist.
+Her granny was an inventor and had a tendency to build things in an overly complicated manner.
+The chicken coop has a digital display showing an encoded number representing the positions of all eggs that could be picked up.
+
+Eliud is asking you to write a program that shows the actual number of eggs in the coop.
+
+The position information encoding is calculated as follows:
+
+1. Scan the potential egg-laying spots and mark down a `1` for an existing egg or a `0` for an empty spot.
+2. Convert the number from binary to decimal.
+3. Show the result on the display.
+
+Example 1:
+
+```text
+Chicken Coop:
+ _ _ _ _ _ _ _
+|E| |E|E| | |E|
+
+Resulting Binary:
+ 1 0 1 1 0 0 1
+
+Decimal number on the display:
+89
+
+Actual eggs in the coop:
+4
+```
+
+Example 2:
+
+```text
+Chicken Coop:
+ _ _ _ _ _ _ _ _
+| | | |E| | | | |
+
+Resulting Binary:
+ 0 0 0 1 0 0 0 0
+
+Decimal number on the display:
+16
+
+Actual eggs in the coop:
+1
+```

exercises/practice/pop-count/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "pop-count.rkt"
+    ],
+    "test": [
+      "pop-count-test.rkt"
+    ],
+    "example": [
+      ".meta/example.rkt"
+    ]
+  },
+  "blurb": "Count the 1 bits in a number",
+  "source": "Christian Willner, Eric Willigers",
+  "source_url": "https://forum.exercism.org/t/new-exercise-suggestion-pop-count/7632/5"
+}

exercises/practice/pop-count/.meta/example.rkt

@@ -0,0 +1,12 @@
+#lang racket
+
+(provide number->eggs)
+
+(define (number->eggs n)
+  (define (recurse val eggs)
+    (define updated (floor (/ val 2)))
+    (or (and (zero? val) eggs)
+        (if (odd? val)
+            (recurse updated (add1 eggs))
+            (recurse updated eggs))))
+  (recurse n 0))

exercises/practice/pop-count/.meta/tests.toml

@@ -0,0 +1,22 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[559e789d-07d1-4422-9004-3b699f83bca3]
+description = "0 eggs"
+
+[97223282-f71e-490c-92f0-b3ec9e275aba]
+description = "1 egg"
+
+[1f8fd18f-26e9-4144-9a0e-57cdfc4f4ff5]
+description = "4 eggs"
+
+[0c18be92-a498-4ef2-bcbb-28ac4b06cb81]
+description = "13 eggs"

exercises/practice/pop-count/pop-count-test.rkt

@@ -0,0 +1,20 @@
+#lang racket/base
+
+(require "pop-count.rkt")
+
+(module+ test
+  (require rackunit rackunit/text-ui)
+
+  (define suite
+    (test-suite
+     "pop count tests"
+
+     (test-equal? "0 eggs" (number->eggs 0) 0)
+
+     (test-equal? "1 egg" (number->eggs 16) 1)
+
+     (test-equal? "4 eggs" (number->eggs 89) 4)
+
+     (test-equal? "13 eggs" (number->eggs 2000000000) 13)))
+
+  (run-tests suite))

exercises/practice/pop-count/pop-count.rkt

@@ -0,0 +1,7 @@
+#lang racket
+
+(provide number->eggs)
+
+(define (number->eggs n)
+  (error "Not implemented yet"))
+