Data commit

Task/Catalan-numbers/Erlang/catalan-numbers.erl

@@ -0,0 +1,30 @@
+-module(catalan).
+
+-export([test/0]).
+
+cat(N) ->
+   factorial(2 * N) div (factorial(N+1) * factorial(N)).
+
+factorial(N) ->
+   fac1(N,1).
+
+fac1(0,Acc) ->
+   Acc;
+fac1(N,Acc) ->
+   fac1(N-1, N * Acc).
+
+cat_r1(0) ->
+   1;
+cat_r1(N) ->
+   lists:sum([cat_r1(I)*cat_r1(N-1-I) || I <- lists:seq(0,N-1)]).
+
+cat_r2(0) ->
+   1;
+cat_r2(N) ->
+   cat_r2(N - 1) * (2 * ((2 * N) - 1)) div (N + 1).
+
+test() ->
+    TestList = lists:seq(0,14),
+    io:format("Directly:\n~p\n",[[cat(N) || N <- TestList]]),
+    io:format("1st recusive method:\n~p\n",[[cat_r1(N) || N <- TestList]]),
+    io:format("2nd recusive method:\n~p\n",[[cat_r2(N) || N <- TestList]]).