New exercise: Pop Count (#190)

* New exercise: Pop Count
* some review suggestions
* remove a tricky sed call

bin/add-exercise

@@ -0,0 +1,99 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if (( $# != 1 )); then
+    echo >&2 "Populates a new directory for a practice exercise."
+    echo >&2 "Usage: $0 <exercise-slug>"
+    exit 1
+fi
+
+die() { echo >&2 "$*"; exit 1; }
+
+required_tool() {
+    command -v "$1" >/dev/null 2>&1 ||
+        die "$1 is required but not installed. Please install it and make sure it's in your PATH."
+}
+required_tool jq
+required_tool curl
+
+[[ -f ./bin/fetch-configlet ]] || die "run this script from the repo's root directory."
+
+slug="${1}"
+
+# transform slug 'resistor-color-duo' to name 'Resistor Color Duo'
+IFS=- read -ra words <<< "${slug}"
+name=${words[*]^}
+
+it_exists=$(
+    jq --arg slug "${slug}" '
+        .exercises.practice
+        | map(select(.slug == $slug))
+        | length > 0
+    ' config.json
+)
+[[ ${it_exists} == false ]] || die "${slug} already exists in config.json"
+
+# Add entry for exercise in config.json
+./bin/fetch-configlet
+jq  --arg slug "${slug}"                 \
+    --arg uuid "$(./bin/configlet uuid)" \
+    --arg name "${name}"                 \
+    '
+        .exercises.practice += [
+            {
+                slug: $slug,
+                name: $name,
+                uuid: $uuid,
+                practices: [],
+                prerequisites: [],
+                difficulty: 1
+            }
+        ]
+    ' config.json > config.json.tmp \
+&& mv config.json.tmp config.json
+
+# Sync the exercise
+./bin/configlet sync --update --yes  \
+                     --tests include \
+                     --metadata      \
+                     --docs          \
+                     --exercise "${slug}"
+
+touch "exercises/practice/${slug}/.meta/example.jq"
+
+echo '"Remove this line and implement your solution" | halt_error' > "exercises/practice/${slug}/${slug}.jq"
+
+echo 
+read -rp 'Your github username: ' author
+conf="exercises/practice/${slug}/.meta/config.json"
+jq  --arg slug "${slug}"     \
+    --arg author "${author}" \
+    '
+        .authors = [$author] |
+        .files = {
+            solution: [$slug + ".jq"],
+            test: ["test-\($slug).bats"],
+            example: [".meta/example.jq"]
+        }
+    ' "${conf}" > "${conf}.tmp" \
+&& mv "${conf}.tmp" "${conf}"
+
+cp exercises/practice/hello-world/bats-extra.bash exercises/practice/"${slug}"
+
+./bin/generate_tests "${slug}"
+
+echo
+find "exercises/practice/${slug}" -type f -ls
+
+cat << NEXT_STEPS
+
+Your next steps are:
+- Review the test suite in 'exercises/practice/${slug}/test-${slug}.jq'
+  - Any test cases you don't implement, mark them in 'exercises/practice/${slug}/.meta/tests.toml' with "include = false"
+- Create the example solution in 'exercises/practice/${slug}/.meta/example.jq'
+- Verify the example solution by running 'bin/validate_one_exercise exercises/practice/${slug}'
+- Review the stub solution in 'exercises/practice/${slug}/${slug}.jq'
+- Update the 'difficulty' value for the exercise's entry in the 'config.json' file
+- Validate CI using 'bin/configlet lint'
+NEXT_STEPS

config.json

@@ -496,6 +496,14 @@
         "practices":     ["conditionals", "numbers", "strings", "compare", "variables", "functions"],
         "prerequisites": ["conditionals", "numbers", "strings", "compare"]
       },
+      {
+        "slug": "pop-count",
+        "name": "Pop Count",
+        "uuid": "551a953d-0f22-4433-8131-dd5606dbc156",
+        "practices": ["recursion"],
+        "prerequisites": ["conditionals"],
+        "difficulty": 2
+      },
       {
         "slug": "gigasecond",
         "name": "Gigasecond",

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": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "pop-count.jq"
+    ],
+    "test": [
+      "test-pop-count.bats"
+    ],
+    "example": [
+      ".meta/example.jq"
+    ]
+  },
+  "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.jq

@@ -0,0 +1,12 @@
+# jq does not have bitwise operators
+
+def count_eggs(count):
+  if . == 0 then
+    count
+  else
+    [(. / 2 | floor), . % 2] as [$next, $bit]
+    | $next | count_eggs(count + $bit)
+  end
+;
+
+.number | count_eggs(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"