Add practice exercise prism

config.json

@@ -2503,6 +2503,31 @@
         ],
         "difficulty": 6
       },
+      {
+        "slug": "prism",
+        "name": "Prism",
+        "uuid": "a2d25eb2-06bb-4e50-8dff-c29582b8e1c6",
+        "practices": [
+          "erlang-libraries",
+          "floating-point-numbers"
+        ],
+        "prerequisites": [
+          "lists",
+          "enum",
+          "maps",
+          "pipe-operator",
+          "recursion",
+          "tail-call-recursion",
+          "pattern-matching",
+          "anonymous-functions",
+          "booleans",
+          "erlang-libraries",
+          "floating-point-numbers",
+          "module-attributes-as-constants",
+          "nil"
+        ],
+        "difficulty": 6
+      },
       {
         "slug": "rail-fence-cipher",
         "name": "Rail Fence Cipher",

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/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

exercises/practice/prism/.gitignore

@@ -0,0 +1,26 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+prism-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jiegillet"
+  ],
+  "files": {
+    "solution": [
+      "lib/prism.ex"
+    ],
+    "test": [
+      "test/prism_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "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/example.ex

@@ -0,0 +1,44 @@
+defmodule Prism do
+  @doc """
+  Finds the sequence of prisms that the laser will hit.
+  """
+
+  @type start :: %{angle: number(), x: number(), y: number()}
+  @type prism :: %{id: integer(), angle: number(), x: number(), y: number()}
+
+  @spec find_sequence(prisms :: [prism()], start :: start()) :: [integer()]
+  def find_sequence(prisms, start) do
+    find_next_prism(start, prisms, [])
+  end
+
+  @precision 0.01
+  defp find_next_prism(start, prisms, sequence) do
+    next_prism =
+      prisms
+      |> Enum.filter(fn %{x: x, y: y} ->
+        different_prism? = x != start.x or y != start.y
+
+        angle_to_prism = :math.atan2(y - start.y, x - start.x) / :math.pi() * 180
+        angle_difference = abs(:math.fmod(angle_to_prism - start.angle, 360))
+
+        pointing_to_prism? =
+          angle_difference < @precision or 360 - angle_difference < @precision
+
+        different_prism? and pointing_to_prism?
+      end)
+      |> Enum.min_by(
+        fn %{x: x, y: y} -> (x - start.x) ** 2 + (y - start.y) ** 2 end,
+        &<=/2,
+        fn -> nil end
+      )
+
+    case next_prism do
+      nil ->
+        Enum.reverse(sequence)
+
+      %{id: id, angle: angle, x: x, y: y} ->
+        next_start = %{angle: start.angle + angle, x: x, y: y}
+        find_next_prism(next_start, prisms, [id | sequence])
+    end
+  end
+end

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/lib/prism.ex

@@ -0,0 +1,12 @@
+defmodule Prism do
+  @doc """
+  Finds the sequence of prisms that the laser will hit.
+  """
+
+  @type start :: %{angle: number(), x: number(), y: number()}
+  @type prism :: %{id: integer(), angle: number(), x: number(), y: number()}
+
+  @spec find_sequence(prisms :: [prism()], start :: start()) :: [integer()]
+  def find_sequence(prisms, start) do
+  end
+end

exercises/practice/prism/mix.exs

@@ -0,0 +1,27 @@
+defmodule Prism.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :prism,
+      version: "0.1.0",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end