Add practice exercise pop-count (#2540)

Author: sanderploegsma

config.json

@@ -1971,6 +1971,18 @@
           "numbers"
         ],
         "difficulty": 5
+      },
+      {
+        "slug": "pop-count",
+        "name": "Pop Count",
+        "uuid": "2d5b6404-3315-48c1-892f-b594a960e7a1",
+        "practices": [
+          "numbers"
+        ],
+        "prerequisites": [
+          "numbers"
+        ],
+        "difficulty": 3
       }
     ]
   },

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 +1,22 @@
+{
+  "authors": [
+    "sanderploegsma"
+  ],
+  "files": {
+    "solution": [
+      "src/main/java/PopCount.java"
+    ],
+    "test": [
+      "src/test/java/PopCountTest.java"
+    ],
+    "example": [
+      ".meta/src/reference/java/PopCount.java"
+    ],
+    "invalidator": [
+      "build.gradle"
+    ]
+  },
+  "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/src/reference/java/PopCount.java

@@ -0,0 +1,15 @@
+public class PopCount {
+    public int eggCount(int number) {
+        var count = 0;
+        var remaining = number;
+
+        while (remaining > 0) {
+            if ((remaining & 1) > 0) {
+                count++;
+            }
+            remaining = remaining >> 1;
+        }
+
+        return count;
+    }
+}

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/build.gradle

@@ -0,0 +1,23 @@
+plugins {
+    id "java"
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation platform("org.junit:junit-bom:5.10.0")
+    testImplementation "org.junit.jupiter:junit-jupiter"
+    testImplementation "org.assertj:assertj-core:3.15.0"
+}
+
+test {
+    useJUnitPlatform()
+
+    testLogging {
+        exceptionFormat = "full"
+        showStandardStreams = true
+        events = ["passed", "failed", "skipped"]
+    }
+}

exercises/practice/pop-count/src/main/java/PopCount.java

@@ -0,0 +1,5 @@
+public class PopCount {
+    public int eggCount(int number) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+}

exercises/practice/pop-count/src/test/java/PopCountTest.java

@@ -0,0 +1,38 @@
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class PopCountTest {
+    @Test
+    @DisplayName("0 eggs")
+    public void test0Eggs() {
+        assertThat(new PopCount().eggCount(0))
+                .isEqualTo(0);
+    }
+
+    @Disabled("Remove to run test")
+    @Test
+    @DisplayName("1 egg")
+    public void test1Egg() {
+        assertThat(new PopCount().eggCount(16))
+                .isEqualTo(1);
+    }
+
+    @Disabled("Remove to run test")
+    @Test
+    @DisplayName("4 eggs")
+    public void test4Eggs() {
+        assertThat(new PopCount().eggCount(89))
+                .isEqualTo(4);
+    }
+
+    @Disabled("Remove to run test")
+    @Test
+    @DisplayName("13 eggs")
+    public void test13Eggs() {
+        assertThat(new PopCount().eggCount(2000000000))
+                .isEqualTo(13);
+    }
+}

exercises/settings.gradle

@@ -95,6 +95,7 @@ include 'practice:perfect-numbers'
 include 'practice:phone-number'
 include 'practice:pig-latin'
 include 'practice:poker'
+include 'practice:pop-count'
 include 'practice:pov'
 include 'practice:prime-factors'
 include 'practice:protein-translation'