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Add practice exercise prism (#1617)
* Add practice exercise `prism` * include latest docs and metadata updates
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‎config.json‎

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

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

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

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

‎exercises/practice/prism/.formatter.exs‎

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# Used by "mix format"
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[
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inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
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]

‎exercises/practice/prism/.gitignore‎

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

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

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{
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"authors": [
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"jiegillet"
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],
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"files": {
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"solution": [
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"lib/prism.ex"
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],
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"test": [
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"test/prism_test.exs"
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],
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"example": [
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".meta/example.ex"
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]
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},
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"blurb": "Calculate the path of a laser through refractive prisms.",
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"source": "FraSanga",
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"source_url": "https://github.com/exercism/problem-specifications/pull/2625"
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}

‎exercises/practice/prism/.meta/example.ex‎

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

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

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[ec65d3b3-f7bf-4015-8156-0609c141c4c4]
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description = "zero prisms"
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[ec0ca17c-0c5f-44fb-89ba-b76395bdaf1c]
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description = "one prism one hit"
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[0db955f2-0a27-4c82-ba67-197bd6202069]
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description = "one prism zero hits"
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[8d92485b-ebc0-4ee9-9b88-cdddb16b52da]
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description = "going up zero hits"
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[78295b3c-7438-492d-8010-9c63f5c223d7]
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description = "going down zero hits"
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[acc723ea-597b-4a50-8d1b-b980fe867d4c]
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description = "going left zero hits"
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[3f19b9df-9eaa-4f18-a2db-76132f466d17]
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description = "negative angle"
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[96dacffb-d821-4cdf-aed8-f152ce063195]
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description = "large angle"
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[513a7caa-957f-4c5d-9820-076842de113c]
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description = "upward refraction two hits"
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[d452b7c7-9761-4ea9-81a9-2de1d73eb9ef]
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description = "downward refraction two hits"
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[be1a2167-bf4c-4834-acc9-e4d68e1a0203]
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description = "same prism twice"
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[df5a60dd-7c7d-4937-ac4f-c832dae79e2e]
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description = "simple path"
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[8d9a3cc8-e846-4a3b-a137-4bfc4aa70bd1]
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description = "multiple prisms floating point precision"
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[e077fc91-4e4a-46b3-a0f5-0ba00321da56]
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description = "complex path with multiple prisms floating point precision"

‎exercises/practice/prism/lib/prism.ex‎

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

‎exercises/practice/prism/mix.exs‎

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

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