feat: solve with bin pattern matching and manual reduce

README.md

@@ -23,6 +23,14 @@ the letters A through Z (either lower or upper case) and whitespace. This way
 data to be encoded will never contain any numbers and numbers inside data to
 be decoded always represent the count for the following character.
 
+## Debugging
+
+- Put `require Logger` at the top of the `RunLengthEncoding` module.
+- Log values to the terminal using `Logger.debug inspect <variable>`.
+- Use the interactive shell to try out things by running `iex -S mix`.
+- In `iex` you can reload your module using `r RunLengthEncoding`
+
+
 ## Running tests
 
 Execute the tests with:
@@ -31,13 +39,6 @@ Execute the tests with:
 $ mix test
 ```
 
-## Debugging
-
-- Put `require Logger` at the top of the `RunLengthEncoding` module.
-- Log values to the terminal using `Logger.debug inspect <variable>`.
-- Use the interactive shell to try out things by running `iex -S mix`.
-
-
 ### Pending tests
 
 In the test suites, all but the first test have been skipped.

lib/run_length_encoding.ex

@@ -9,8 +9,42 @@ defmodule RunLengthEncoding do
   require Logger
 
   def encode(string) do
+    string
+    |> encode_rec(0)
   end
 
+  defp encode_rec(<<a::utf8, b::utf8>> <> rest, count) when a == b do
+    encode_rec(<<b::utf8>> <> rest, count + 1)
+  end
+
+  defp encode_rec(<<a::utf8>> <> rest, count) when count == 0 do
+    <<a::utf8>> <> encode_rec(rest, 0)
+  end
+
+  defp encode_rec(<<a::utf8>> <> rest, count) do
+    to_string(count + 1) <> <<a::utf8>> <> encode_rec(rest, 0)
+  end
+
+  defp encode_rec(rest, _), do: rest
+
   def decode(string) do
+    string
+    |> decode_rec(0)
   end
+
+  defguard is_digit(char) when ?0 <= char and char <= ?9
+
+  defp decode_rec(<<a::utf8>> <> rest, times) when is_digit(a) do
+    decode_rec(rest, times * 10 + String.to_integer(<<a>>))
+  end
+
+  defp decode_rec(<<a::utf8>> <> rest, 0) do
+    <<a>> <> decode_rec(rest, 0)
+  end
+
+  defp decode_rec(<<a::utf8>> <> rest, times) do
+    String.duplicate(<<a>>, times) <> decode_rec(rest, 0)
+  end
+
+  defp decode_rec(rest, _), do: rest
 end

test/run_length_encoding_test.exs

@@ -6,64 +6,52 @@ defmodule RunLengthEncodingTest do
     assert RunLengthEncoding.encode("") === ""
   end
 
-  @tag :pending
   test "encode single characters only are encoded without count" do
     assert RunLengthEncoding.encode("XYZ") === "XYZ"
   end
 
-  @tag :pending
   test "encode string with no single characters" do
     assert RunLengthEncoding.encode("AABBBCCCC") == "2A3B4C"
   end
 
-  @tag :pending
   test "encode single characters mixed with repeated characters" do
     assert RunLengthEncoding.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB") ===
              "12WB12W3B24WB"
   end
 
-  @tag :pending
   test "encode multiple whitespace mixed in string" do
     assert RunLengthEncoding.encode("  hsqq qww  ") === "2 hs2q q2w2 "
   end
 
-  @tag :pending
   test "encode lowercase characters" do
     assert RunLengthEncoding.encode("aabbbcccc") === "2a3b4c"
   end
 
-  @tag :pending
   test "decode empty string" do
     assert RunLengthEncoding.decode("") === ""
   end
 
-  @tag :pending
   test "decode single characters only" do
     assert RunLengthEncoding.decode("XYZ") === "XYZ"
   end
 
-  @tag :pending
   test "decode string with no single characters" do
     assert RunLengthEncoding.decode("2A3B4C") == "AABBBCCCC"
   end
 
-  @tag :pending
   test "decode single characters with repeated characters" do
     assert RunLengthEncoding.decode("12WB12W3B24WB") ===
              "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
   end
 
-  @tag :pending
   test "decode multiple whitespace mixed in string" do
     assert RunLengthEncoding.decode("2 hs2q q2w2 ") === "  hsqq qww  "
   end
 
-  @tag :pending
   test "decode lower case string" do
     assert RunLengthEncoding.decode("2a3b4c") === "aabbbcccc"
   end
 
-  @tag :pending
   test "encode followed by decode gives original string" do
     original = "zzz ZZ  zZ"
     encoded = RunLengthEncoding.encode(original)