Philip + Christoph

.gitignore

@@ -22,3 +22,4 @@ erl_crash.dump
 # Ignore package tarball (built via "mix hex.build").
 run_length_encoding-*.tar
 
+.tool-versions

lib/run_length_encoding.ex

@@ -8,9 +8,63 @@ defmodule RunLengthEncoding do
   """
   require Logger
 
+
+  # accu :: [ { char, count:int } ]
+  # [ { "A", 2 }, { "B", 1 } ]
+  defp encode_rec([], accu), do: accu
+  defp encode_rec([h | t], [{h, count} | accu]), do: encode_rec(t, [{h, count + 1} | accu])
+  defp encode_rec([h | t], [{old, count} | accu]), do: encode_rec(t, [{h, 1} | [{old, count} | accu]])
+  defp encode_rec([h | t], []), do: encode_rec(t, [{h, 1}])
+
+  defp rle_char({char, 1}, result), do: char <> result
+  defp rle_char({char, count}, result), do: "#{count}" <> char <> result
+
+  defp encode_assemble(tuples) do
+    tuples
+    |> Enum.reduce("", &rle_char/2)
+  end
+
   def encode(string) do
+    encode_rec(String.codepoints(string), [])
+    |> encode_assemble
+  end
+
+
+
+
+
+
+
+
+  @digits 0..9
+          |> Enum.map(&to_string/1)
+
+  # accu :: { reverse_digits:[char], [ { reverse_digits:[char], char } ] }
+  # { [], [ { ["1","2"], "A" } ] }
+  defp decode_rec([], accu), do: accu
+  defp decode_rec([h | t], {number, accu}) when not (h in @digits), do: decode_rec(t, {[], [{number, h} | accu]})
+  defp decode_rec([h | t], {number, accu}), do: decode_rec(t, {[h | number], accu})
+
+  defp digits_to_int([]), do: 1
+  defp digits_to_int(digits),
+       do: digits
+           |> Enum.join("")
+           |> String.to_integer
+
+  defp rldecode_char({reverse_digits, char}, result) do
+    count = reverse_digits
+            |> Enum.reverse
+            |> digits_to_int
+    String.duplicate(char, count) <> result
+  end
+
+  defp decode_assemble({_, chars}) do
+    chars
+    |> Enum.reduce("", &rldecode_char/2)
   end
 
   def decode(string) do
+    decode_rec(String.codepoints(string), {[], []})
+    |> decode_assemble
   end
 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)