Make run-length-encoding exercise expected values consistent with README (#293)

* omit '1' on single-letter runs (fixes #292)

* use test cases from canonical-data.json

* replace incorrect example in doc string

* update example solution to work with lowercase letters and whitespace

Author: daveyarwood

exercises/run-length-encoding/example.exs

@@ -2,13 +2,24 @@ defmodule RunLengthEncoder do
 
   @spec encode(String.t) :: String.t
   def encode(string) do
-    Regex.scan(~r/([A-Z])\1*/, string)
-    |> Enum.map_join(fn([run, c]) -> "#{String.length(run)}#{c}" end)
+    Regex.scan(~r/([a-zA-Z ])\1*/, string)
+    |> Enum.map_join(fn([run, c]) ->
+      if String.match?(run, ~r/\s+/) do
+        run
+      else
+        times = String.length(run)
+        number = if times == 1 do "" else times end
+          "#{number}#{c}"
+      end
+    end)
   end
 
   @spec decode(String.t) :: String.t
   def decode(string) do
-    Regex.scan(~r/(\d+)(.)/, string)
-    |> Enum.map_join(fn [_,n,c] -> String.duplicate(c, String.to_integer(n)) end)
+    Regex.scan(~r/(\d*)(.)/, string)
+    |> Enum.map_join(fn [_,n,c] ->
+      times = if n == "" do 1 else String.to_integer(n) end
+      String.duplicate(c, times)
+    end)
   end
 end

exercises/run-length-encoding/rle.exs

@@ -1,10 +1,10 @@
 defmodule RunLengthEncoder do
   @doc """
   Generates a string where consecutive elements are represented as a data value and count.
-  "HORSE" => "1H1O1R1S1E"
+  "AABBBCCCC" => "2A3B4C"
   For this example, assume all input are strings, that are all uppercase letters.
   It should also be able to reconstruct the data into its original form.
-  "1H1O1R1S1E" => "HORSE"
+  "2A3B4C" => "AABBBCCCC"
   """
   @spec encode(String.t) :: String.t
   def encode(string) do

exercises/run-length-encoding/rle_test.exs

@@ -8,32 +8,49 @@ ExUnit.configure exclude: :pending, trace: true
 defmodule RunLengthEncoderTest do
   use ExUnit.Case
 
-  test "empty string returns empty" do
+  test "encode empty string" do
     assert RunLengthEncoder.encode("") === ""
   end
 
   @tag :pending
-  test "simple string gets encoded" do
-    assert RunLengthEncoder.encode("AAA") === "3A"
+  test "encode single characters only" do
+    assert RunLengthEncoder.encode("XYZ") === "XYZ"
   end
 
   @tag :pending
-  test "more complicated string" do
-    assert RunLengthEncoder.encode("HORSE") == "1H1O1R1S1E"
+  test "decode empty string" do
+    assert RunLengthEncoder.decode("") === ""
   end
 
   @tag :pending
-  test "an even more complex string" do
-    assert RunLengthEncoder.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB") === "12W1B12W3B24W1B"
+  test "decode single characters only" do
+    assert RunLengthEncoder.decode("XYZ") === "XYZ"
   end
 
   @tag :pending
-  test "it decodes an encoded simple string" do
-    assert RunLengthEncoder.decode("3A") === "AAA"
+  test "encode simple" do
+    assert RunLengthEncoder.encode("AABBBCCCC") == "2A3B4C"
   end
 
   @tag :pending
-  test "it decodes a more complicated string" do
-    assert RunLengthEncoder.decode("12W1B12W3B24W1B") === "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
+  test "decode simple" do
+    assert RunLengthEncoder.decode("2A3B4C") == "AABBBCCCC"
+  end
+
+  @tag :pending
+  test "encode with single values" do
+    assert RunLengthEncoder.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB") === "12WB12W3B24WB"
+  end
+
+  @tag :pending
+  test "decode with single values" do
+    assert RunLengthEncoder.decode("12WB12W3B24WB") === "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
+  end
+
+  @tag :pending
+  test "decode(encode(...)) combination" do
+    original = "zzz ZZ  zZ"
+    encoded = RunLengthEncoder.encode(original)
+    assert RunLengthEncoder.decode(encoded) === original
   end
 end