Add resistor-color-trio exercise (#389)

config.json

@@ -912,6 +912,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "resistor-color-trio",
+        "name": "Resistor Color Trio",
+        "uuid": "63ad9b99-31c2-47d6-9f66-ab803a1969dd",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },

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

@@ -0,0 +1,56 @@
+# Instructions
+
+If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
+For this exercise, you need to know only three things about them:
+
+- Each resistor has a resistance value.
+- Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
+  To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
+- Each band acts as a digit of a number.
+  For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
+  In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands.
+  The program will take 3 colors as input, and outputs the correct value, in ohms.
+  The color bands are encoded as follows:
+
+- black: 0
+- brown: 1
+- red: 2
+- orange: 3
+- yellow: 4
+- green: 5
+- blue: 6
+- violet: 7
+- grey: 8
+- white: 9
+
+In Resistor Color Duo you decoded the first two colors.
+For instance: orange-orange got the main value `33`.
+The third color stands for how many zeros need to be added to the main value.
+The main value plus the zeros gives us a value in ohms.
+For the exercise it doesn't matter what ohms really are.
+For example:
+
+- orange-orange-black would be 33 and no zeros, which becomes 33 ohms.
+- orange-orange-red would be 33 and 2 zeros, which becomes 3300 ohms.
+- orange-orange-orange would be 33 and 3 zeros, which becomes 33000 ohms.
+
+(If Math is your thing, you may want to think of the zeros as exponents of 10.
+If Math is not your thing, go with the zeros.
+It really is the same thing, just in plain English instead of Math lingo.)
+
+This exercise is about translating the colors into a label:
+
+> "... ohms"
+
+So an input of `"orange", "orange", "black"` should return:
+
+> "33 ohms"
+
+When we get to larger resistors, a [metric prefix][metric-prefix] is used to indicate a larger magnitude of ohms, such as "kiloohms".
+That is similar to saying "2 kilometers" instead of "2000 meters", or "2 kilograms" for "2000 grams".
+
+For example, an input of `"orange", "orange", "orange"` should return:
+
+> "33 kiloohms"
+
+[metric-prefix]: https://en.wikipedia.org/wiki/Metric_prefix

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "resistor-color-trio.R"
+    ],
+    "test": [
+      "test_resistor-color-trio.R"
+    ],
+    "example": [
+      ".meta/example.R"
+    ]
+  },
+  "blurb": "Convert color codes, as used on resistors, to a human-readable label.",
+  "source": "Maud de Vries, Erik Schierboom",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/1549"
+}

exercises/practice/resistor-color-trio/.meta/example.R

@@ -0,0 +1,16 @@
+colors <- c("black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white") # nolint
+units <- c("gigaohms" = 1e9, "megaohms" = 1e6, "kiloohms" = 1e3, "ohms" = 0)
+
+value <- function(resistor_colors) {
+  sum((match(resistor_colors[1:2], colors) - 1) * c(10, 1))
+}
+
+ohms <- function(resistor_colors) {
+  value(resistor_colors) * 10^(match(resistor_colors[3], colors) - 1)
+}
+
+label <- function(resistor_colors) {
+  resistor_ohms <- ohms(resistor_colors)
+  unit_idx <- which.max(resistor_ohms >= units)
+  paste(resistor_ohms / 1000^(3:0)[[unit_idx]], names(unit_idx), sep = " ")
+}

exercises/practice/resistor-color-trio/.meta/tests.toml

@@ -0,0 +1,40 @@
+# 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.
+
+[d6863355-15b7-40bb-abe0-bfb1a25512ed]
+description = "Orange and orange and black"
+
+[1224a3a9-8c8e-4032-843a-5224e04647d6]
+description = "Blue and grey and brown"
+
+[b8bda7dc-6b95-4539-abb2-2ad51d66a207]
+description = "Red and black and red"
+
+[5b1e74bc-d838-4eda-bbb3-eaba988e733b]
+description = "Green and brown and orange"
+
+[f5d37ef9-1919-4719-a90d-a33c5a6934c9]
+description = "Yellow and violet and yellow"
+
+[5f6404a7-5bb3-4283-877d-3d39bcc33854]
+description = "Blue and violet and blue"
+
+[7d3a6ab8-e40e-46c3-98b1-91639fff2344]
+description = "Minimum possible value"
+
+[ca0aa0ac-3825-42de-9f07-dac68cc580fd]
+description = "Maximum possible value"
+
+[0061a76c-903a-4714-8ce2-f26ce23b0e09]
+description = "First two colors make an invalid octal number"
+
+[30872c92-f567-4b69-a105-8455611c10c4]
+description = "Ignore extra colors"

exercises/practice/resistor-color-trio/resistor-color-trio.R

@@ -0,0 +1,3 @@
+label <- function(resistor_colors) {
+
+}

exercises/practice/resistor-color-trio/test_resistor-color-trio.R

@@ -0,0 +1,42 @@
+source("./resistor-color-trio.R")
+library(testthat)
+
+test_that("Orange and orange and black", {
+  expect_equal(label(c("orange", "orange", "black")), "33 ohms")
+})
+
+test_that("Blue and grey and brown", {
+  expect_equal(label(c("blue", "grey", "brown")), "680 ohms")
+})
+
+test_that("Red and black and red", {
+  expect_equal(label(c("red", "black", "red")), "2 kiloohms")
+})
+
+test_that("Green and brown and orange", {
+  expect_equal(label(c("green", "brown", "orange")), "51 kiloohms")
+})
+
+test_that("Yellow and violet and yellow", {
+  expect_equal(label(c("yellow", "violet", "yellow")), "470 kiloohms")
+})
+
+test_that("Blue and violet and blue", {
+  expect_equal(label(c("blue", "violet", "blue")), "67 megaohms")
+})
+
+test_that("Minimum possible value", {
+  expect_equal(label(c("black", "black", "black")), "0 ohms")
+})
+
+test_that("Maximum possible value", {
+  expect_equal(label(c("white", "white", "white")), "99 gigaohms")
+})
+
+test_that("First two colors make an invalid octal number", {
+  expect_equal(label(c("black", "grey", "black")), "8 ohms")
+})
+
+test_that("Ignore extra colors", {
+  expect_equal(label(c("blue", "green", "yellow", "orange")), "650 kiloohms")
+})