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Add resistor-color-trio (#747)
* Add `resistor-color-trio` * Apply more suggestions
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‎config.json‎

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],
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"difficulty": 2
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},
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{
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"slug": "resistor-color-trio",
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"name": "Resistor Color Trio",
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"uuid": "761f7552-c192-4d46-a21c-fa30c4788307",
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"practices": [
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"lists",
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"pattern-matching"
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],
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"prerequisites": [
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"lists",
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"basics-2",
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"custom-types",
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"pattern-matching"
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],
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"difficulty": 3
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},
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{
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"slug": "space-age",
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"name": "Space Age",

‎exercises/practice/resistor-color-trio/.docs/instructions.md‎

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# Instructions
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If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
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For this exercise, you need to know only three things about them:
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- Each resistor has a resistance value.
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- Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
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To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
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- Each band acts as a digit of a number.
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For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
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In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands.
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The program will take 3 colors as input, and outputs the correct value, in ohms.
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The color bands are encoded as follows:
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- black: 0
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- brown: 1
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- red: 2
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- orange: 3
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- yellow: 4
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- green: 5
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- blue: 6
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- violet: 7
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- grey: 8
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- white: 9
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In Resistor Color Duo you decoded the first two colors.
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For instance: orange-orange got the main value `33`.
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The third color stands for how many zeros need to be added to the main value.
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The main value plus the zeros gives us a value in ohms.
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For the exercise it doesn't matter what ohms really are.
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For example:
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- orange-orange-black would be 33 and no zeros, which becomes 33 ohms.
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- orange-orange-red would be 33 and 2 zeros, which becomes 3300 ohms.
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- orange-orange-orange would be 33 and 3 zeros, which becomes 33000 ohms.
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(If Math is your thing, you may want to think of the zeros as exponents of 10.
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If Math is not your thing, go with the zeros.
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It really is the same thing, just in plain English instead of Math lingo.)
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This exercise is about translating the colors into a label:
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> "... ohms"
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So an input of `"orange", "orange", "black"` should return:
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> "33 ohms"
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When we get to larger resistors, a [metric prefix][metric-prefix] is used to indicate a larger magnitude of ohms, such as "kiloohms".
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That is similar to saying "2 kilometers" instead of "2000 meters", or "2 kilograms" for "2000 grams".
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For example, an input of `"orange", "orange", "orange"` should return:
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> "33 kiloohms"
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[metric-prefix]: https://en.wikipedia.org/wiki/Metric_prefix

‎exercises/practice/resistor-color-trio/.meta/config.json‎

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{
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"authors": [
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"BNAndras"
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],
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"files": {
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"solution": [
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"src/ResistorColorTrio.elm"
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],
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"test": [
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"tests/Tests.elm"
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],
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"example": [
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".meta/src/ResistorColorTrio.example.elm"
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]
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},
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"blurb": "Convert color codes, as used on resistors, to a human-readable label.",
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"source": "Maud de Vries, Erik Schierboom",
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"source_url": "https://github.com/exercism/problem-specifications/issues/1549"
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}

‎exercises/practice/resistor-color-trio/.meta/src/ResistorColorTrio.example.elm‎

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module ResistorColorTrio exposing (Color(..), label)
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type Color
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= Black
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| Brown
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| Red
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| Orange
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| Yellow
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| Green
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| Blue
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| Violet
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| Grey
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| White
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label : List Color -> String
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label colors =
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let
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( magnitude, unit ) =
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colors |> totalResistance |> formatted
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in
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String.fromInt magnitude ++ " " ++ unit
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formatted : Int -> ( Int, String )
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formatted resistance =
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if resistance < 1000 then
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( resistance, "ohms" )
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else if resistance < 1000000 then
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( resistance // 1000, "kiloohms" )
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else if resistance < 1000000000 then
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( resistance // 1000000, "megaohms" )
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else
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( resistance // 1000000000, "gigaohms" )
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totalResistance : List Color -> Int
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totalResistance colors =
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case colors of
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first :: second :: third :: _ ->
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(bandValue first * 10 + bandValue second) * 10 ^ bandValue third
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first :: second :: [] ->
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bandValue first * 10 + bandValue second
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first :: [] ->
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bandValue first
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_ ->
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-1
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bandValue : Color -> Int
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bandValue color =
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case color of
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Black ->
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0
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Brown ->
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1
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Red ->
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2
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Orange ->
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3
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Yellow ->
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4
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Green ->
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5
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Blue ->
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6
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Violet ->
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7
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Grey ->
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8
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White ->
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9

‎exercises/practice/resistor-color-trio/.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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[d6863355-15b7-40bb-abe0-bfb1a25512ed]
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description = "Orange and orange and black"
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[1224a3a9-8c8e-4032-843a-5224e04647d6]
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description = "Blue and grey and brown"
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[b8bda7dc-6b95-4539-abb2-2ad51d66a207]
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description = "Red and black and red"
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[5b1e74bc-d838-4eda-bbb3-eaba988e733b]
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description = "Green and brown and orange"
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[f5d37ef9-1919-4719-a90d-a33c5a6934c9]
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description = "Yellow and violet and yellow"
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[5f6404a7-5bb3-4283-877d-3d39bcc33854]
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description = "Blue and violet and blue"
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[7d3a6ab8-e40e-46c3-98b1-91639fff2344]
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description = "Minimum possible value"
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[ca0aa0ac-3825-42de-9f07-dac68cc580fd]
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description = "Maximum possible value"
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[0061a76c-903a-4714-8ce2-f26ce23b0e09]
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description = "First two colors make an invalid octal number"
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[30872c92-f567-4b69-a105-8455611c10c4]
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description = "Ignore extra colors"

‎exercises/practice/resistor-color-trio/elm.json‎

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{
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"type": "application",
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"source-directories": [
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"src"
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],
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"elm-version": "0.19.1",
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"dependencies": {
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"direct": {
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"elm/core": "1.0.5",
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"elm/json": "1.1.3",
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"elm/parser": "1.1.0",
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"elm/random": "1.0.0",
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"elm/regex": "1.0.0",
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"elm/time": "1.0.0",
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"elm/html": "1.0.0"
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},
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"indirect": {}
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},
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"test-dependencies": {
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"direct": {
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"elm-explorations/test": "2.1.0",
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"rtfeldman/elm-iso8601-date-strings": "1.1.4"
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},
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"indirect": {
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"elm/bytes": "1.0.8",
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"elm/virtual-dom": "1.0.3"
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}
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}
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}

‎exercises/practice/resistor-color-trio/src/ResistorColorTrio.elm‎

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module ResistorColorTrio exposing (Color(..), label)
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type Color
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= Black
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| Brown
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| Red
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| Orange
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| Yellow
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| Green
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| Blue
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| Violet
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| Grey
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| White
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label : List Color -> String
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label colors =
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Debug.todo "Please implement label"

‎exercises/practice/resistor-color-trio/tests/Tests.elm‎

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module Tests exposing (tests)
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import Expect
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import ResistorColorTrio exposing (Color(..), label)
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import Test exposing (Test, describe, skip, test)
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tests : Test
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tests =
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describe "ResistorColorTrio"
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[ test "Orange and orange and black" <|
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\() ->
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ResistorColorTrio.label [ Orange, Orange, Black ]
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|> Expect.equal "33 ohms"
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, skip <|
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test "Blue and grey and brown" <|
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\() ->
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ResistorColorTrio.label [ Blue, Grey, Brown ]
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|> Expect.equal "680 ohms"
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, skip <|
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test "Red and black and red" <|
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\() ->
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ResistorColorTrio.label [ Red, Black, Red ]
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|> Expect.equal "2 kiloohms"
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, skip <|
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test "Green and brown and orange" <|
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\() ->
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ResistorColorTrio.label [ Green, Brown, Orange ]
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|> Expect.equal "51 kiloohms"
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, skip <|
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test "Yellow and violet and yellow" <|
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\() ->
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ResistorColorTrio.label [ Yellow, Violet, Yellow ]
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|> Expect.equal "470 kiloohms"
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, skip <|
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test "Blue and violet and blue" <|
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\() ->
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ResistorColorTrio.label [ Blue, Violet, Blue ]
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|> Expect.equal "67 megaohms"
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, skip <|
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test "Minimum possible value" <|
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\() ->
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ResistorColorTrio.label [ Black, Black, Black ]
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|> Expect.equal "0 ohms"
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, skip <|
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test "Maximum possible value" <|
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\() ->
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ResistorColorTrio.label [ White, White, White ]
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|> Expect.equal "99 gigaohms"
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, skip <|
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test "First two colors make an invalid octal number" <|
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\() ->
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ResistorColorTrio.label [ Black, Grey, Black ]
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|> Expect.equal "8 ohms"
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, skip <|
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test "Ignore extra colors" <|
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\() ->
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ResistorColorTrio.label [ Blue, Green, Yellow, Orange ]
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|> Expect.equal "650 kiloohms"
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]

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