Add Prism exercise

Author: kahgoh

config.json

@@ -799,6 +799,16 @@
         ],
         "difficulty": 4
       },
+      {
+        "slug": "prism",
+        "name": "Prism",
+        "uuid": "1fca8759-0236-493c-a4ef-2807cb33fd2b",
+        "practices": [],
+        "prerequisites": [
+          "lists"
+        ],
+        "difficulty": 4
+      },
       {
         "slug": "proverb",
         "name": "Proverb",

exercises/practice/prism/.docs/instructions.md

@@ -0,0 +1,38 @@
+# Instructions
+
+Before activating the laser array, you must predict the exact order in which crystals will be hit, identified by their sample IDs.
+
+## Example Test Case
+
+Consider this crystal array configuration:
+
+```json
+{
+  "start": { "x": 0, "y": 0, "angle": 0 },
+  "prisms": [
+    { "id": 1, "x": 10, "y": 10, "angle": -90 },
+    { "id": 2, "x": 10, "y": 0, "angle": 90 },
+    { "id": 3, "x": 30, "y": 10, "angle": 45 },
+    { "id": 4, "x": 20, "y": 0, "angle": 0 }
+  ]
+}
+```
+
+## What's Happening
+
+The laser starts at the origin `(0, 0)` and fires horizontally to the right at angle 0°.
+Here's the step-by-step beam path:
+
+**Step 1**: The beam travels along the x-axis (y = 0) and first encounters **Crystal #2** at position `(10, 0)`.
+This crystal has a refraction angle of 90°, which means it bends the beam perpendicular to its current path.
+The beam, originally traveling at 0°, is now redirected to 90° (straight up).
+
+**Step 2**: The beam now travels vertically upward from position `(10, 0)` and strikes **Crystal #1** at position `(10, 10)`.
+This crystal has a refraction angle of -90°, bending the beam by -90° relative to its current direction.
+The beam was traveling at 90°, so after refraction it's now at 0° (90° + (-90°) = 0°), traveling horizontally to the right again.
+
+**Step 3**: From position `(10, 10)`, the beam travels horizontally and encounters **Crystal #3** at position `(30, 10)`.
+This crystal refracts the beam by 45°, changing its direction to 45°.
+The beam continues into empty space beyond the array.
+
+!["A graph showing the path of a laser beam refracted through three prisms."](https://assets.exercism.org/images/exercises/prism/laser_path-light.svg)

exercises/practice/prism/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You're a researcher at **PRISM** (Precariously Redirected Illumination Safety Management), working with a precision laser calibration system that tests experimental crystal prisms.
+These crystals are being developed for next-generation optical computers, and each one has unique refractive properties based on its molecular structure.
+The lab's laser system can damage crystals if they receive unexpected illumination, so precise path prediction is critical.

exercises/practice/prism/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "src/main/java/Prism.java"
+    ],
+    "test": [
+      "src/test/java/PrismTest.java"
+    ],
+    "example": [
+      ".meta/src/reference/java/Prism.java"
+    ]
+  },
+  "blurb": "Calculate the path of a laser through refractive prisms.",
+  "source": "FraSanga",
+  "source_url": "https://github.com/exercism/problem-specifications/pull/2625"
+}

exercises/practice/prism/.meta/src/reference/java/Prism.java

@@ -0,0 +1,88 @@
+import java.util.*;
+import java.util.function.Predicate;
+
+public class Prism {
+
+    public record LaserInfo(double x, double y, double angle, Integer prismId) {
+        public LaserInfo(double x, double y, double angle) {
+            this(x, y, angle, null);
+        }
+    }
+
+    public record PrismInfo(int id, double x, double y, double angle) {
+    }
+
+    private static final int DECIMAL_PLACES = 3;
+
+    private static final double ROUND_FACTOR = Math.pow(10, DECIMAL_PLACES);
+
+    public static List<Integer> findSequence(LaserInfo laser, List<PrismInfo> prisms) {
+        LaserInfo last = laser;
+        Optional<PrismInfo> lastPrism = Optional.empty();
+        List<Integer> sequence = new ArrayList<>();
+
+        do {
+            lastPrism = prisms.stream().filter(new TouchesPrism(last)).min(new CompareDistance(last));
+            if (lastPrism.isPresent()) {
+                PrismInfo nextPrism = lastPrism.get();
+                sequence.add(nextPrism.id);
+                last = new LaserInfo(nextPrism.x, nextPrism.y,
+                        normalizeDegrees(nextPrism.angle + last.angle), nextPrism.id);
+            }
+        } while (lastPrism.isPresent());
+        return sequence;
+    }
+
+    private static double normalizeDegrees(double degrees) {
+        if (degrees < 0) {
+            return (degrees % 360) + 360;
+        }
+        return degrees % 360;
+    }
+
+    private static class CompareDistance implements Comparator<PrismInfo> {
+        private final LaserInfo laser;
+
+        public CompareDistance(LaserInfo laser) {
+            this.laser = laser;
+        }
+
+        @Override
+        public int compare(PrismInfo o1, PrismInfo o2) {
+            final double d1 = Math.hypot(o1.x - laser.x, o1.y - laser.y);
+            final double d2 = Math.hypot(o2.x - laser.x, o2.y - laser.y);
+            return Double.compare(d1, d2);
+        }
+    }
+
+    private static class TouchesPrism implements Predicate<PrismInfo> {
+        private final LaserInfo laser;
+        private final double sinAngle;
+        private final double cosAngle;
+
+        public TouchesPrism(LaserInfo laser) {
+            this.laser = laser;
+
+            double angleRadians = Math.toRadians(laser.angle);
+            this.sinAngle = Math.sin(angleRadians);
+            this.cosAngle = Math.cos(angleRadians);
+        }
+
+        @Override
+        public boolean test(PrismInfo prism) {
+            if (laser.prismId != null && laser.prismId == prism.id) {
+                return false;
+            }
+
+            double dx = prism.x - laser.x;
+            double dy = prism.y - laser.y;
+            double hyp = Math.hypot(dx, dy);
+
+            return isClose(hyp * cosAngle, dx) && isClose(hyp * sinAngle, dy);
+        }
+    }
+
+    private static boolean isClose(double a, double b) {
+        return Math.abs(Math.round(a * ROUND_FACTOR - b * ROUND_FACTOR)) <= 1;
+    }
+}

exercises/practice/prism/.meta/tests.toml

@@ -0,0 +1,52 @@
+# 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.
+
+[ec65d3b3-f7bf-4015-8156-0609c141c4c4]
+description = "zero prisms"
+
+[ec0ca17c-0c5f-44fb-89ba-b76395bdaf1c]
+description = "one prism one hit"
+
+[0db955f2-0a27-4c82-ba67-197bd6202069]
+description = "one prism zero hits"
+
+[8d92485b-ebc0-4ee9-9b88-cdddb16b52da]
+description = "going up zero hits"
+
+[78295b3c-7438-492d-8010-9c63f5c223d7]
+description = "going down zero hits"
+
+[acc723ea-597b-4a50-8d1b-b980fe867d4c]
+description = "going left zero hits"
+
+[3f19b9df-9eaa-4f18-a2db-76132f466d17]
+description = "negative angle"
+
+[96dacffb-d821-4cdf-aed8-f152ce063195]
+description = "large angle"
+
+[513a7caa-957f-4c5d-9820-076842de113c]
+description = "upward refraction two hits"
+
+[d452b7c7-9761-4ea9-81a9-2de1d73eb9ef]
+description = "downward refraction two hits"
+
+[be1a2167-bf4c-4834-acc9-e4d68e1a0203]
+description = "same prism twice"
+
+[df5a60dd-7c7d-4937-ac4f-c832dae79e2e]
+description = "simple path"
+
+[8d9a3cc8-e846-4a3b-a137-4bfc4aa70bd1]
+description = "multiple prisms floating point precision"
+
+[e077fc91-4e4a-46b3-a0f5-0ba00321da56]
+description = "complex path with multiple prisms floating point precision"

exercises/practice/prism/build.gradle

@@ -0,0 +1,25 @@
+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:3.25.1"
+
+    testRuntimeOnly "org.junit.platform:junit-platform-launcher"
+}
+
+test {
+    useJUnitPlatform()
+
+    testLogging {
+        exceptionFormat = "full"
+        showStandardStreams = true
+        events = ["passed", "failed", "skipped"]
+    }
+}

exercises/practice/prism/gradle/wrapper/gradle-wrapper.jar

@@ -0,0 +1,6 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.3.1-bin.zip
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists