FutureLearn - recursion

recursion.erl

-module(recursion).
-export([fac/1,fib/1,pieces/1,multipieces/2]).

fac(0) -> 1;
fac(N) when N>0 -> fac(N-1)*N.

fib(0) -> 0;
fib(1) -> 1;
fib(N) ->
  fib(N-1)+fib(N-2).

% fib(4) = fib(4-1) + fib(4-2)
% fib(4) = fib(3) + fib(2)
% fib(4) = 2 + 1
% fib(4) = 3

pieces(0) -> 1;
pieces(1) -> 2;
pieces(N) -> pieces(N-1) + N.

multipieces(0,_) -> 1;
multipieces(X,1) -> X+1;
multipieces(X,N) ->
  multipieces(X-1,N) + multipieces(X-1,N-1).