--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rps5.erl	Wed Feb 26 19:05:32 2014 +0900
@@ -0,0 +1,85 @@
+-module(rps5).
+-export([
+    get_rules/0,
+    beats/1, test_beats/0,
+    loses/1, test_loses/0,
+    winning_hand/1, test_winning_hand/0]).
+
+get_rules() -> [rock, paper, scissors, spock, lizard].
+
+beats(rock) ->
+    [scissors, lizard];
+
+beats(paper) ->
+    [spock, rock];
+
+beats(scissors) ->
+    [lizard, paper];
+
+beats(spock) ->
+    [rock, scissors];
+
+beats(lizard) ->
+    [paper, spock].
+
+loses(lizard) ->
+    [scissors, rock];
+
+loses(spock) ->
+    [paper, lizard];
+
+loses(scissors) ->
+    [rock, spock];
+
+loses(paper) ->
+    [lizard, scissors];
+
+loses(rock) ->
+    [spock, paper].
+
+test_beats() ->
+    lists:foreach(
+        fun(H) ->
+            io:format("~w beats ~w.~n", [H, beats(H)])
+        end,
+        get_rules()).
+
+test_loses() ->
+    lists:foreach(
+        fun(H) ->
+            io:format("~w loses to ~w.~n", [H, loses(H)])
+        end,
+        get_rules()).
+
+% winner for 3 hands is:
+% rock, rock, rock      -> rock
+% rock, paper, scissors -> undefined
+% rock, paper, paper    -> paper
+% rock, rock, paper     -> paper
+
+winning_hand(Hands) ->
+    HSet = sets:from_list(Hands),
+    sets:fold(
+        fun(Hand, Acc) ->
+            Loses = loses(Hand),
+            case sets:is_disjoint(sets:from_list(Loses), HSet) of
+                true -> Hand;
+                false -> Acc
+            end
+        end, undefined, HSet).
+
+test_winning_hand() ->
+    Exclude = fun(Hand) -> lists:delete(Hand, get_rules()) end,
+    Cases = [
+             [rock, rock, rock],
+             [rock, paper, scissors],
+             [rock, paper, paper],
+             [rock, rock, paper]
+             |lists:map(Exclude, get_rules())
+            ],
+    lists:foreach(
+        fun(Hands) ->
+            Winner = winning_hand(Hands),
+            io:format("~w wins in ~w.~n", [Winner, Hands])
+        end,
+        Cases).