Coins problem in Erlang

Question

How many different ways can 200 be made using any number of coins? The possible denominations are 1, 2, 5, 10, 20, 50, 100, 200.

-module(coins).
-export([coins/2]).
coins(_, 0) -> 1;
coins([], _) -> 0;
coins(_, Goal) when Goal < 0 -> 0;
coins([H|T], Goal) ->
 coins([H|T], Goal-H) + coins(T, Goal).

The call is:

1> c(coins).
2> coins:coins([1, 2, 5, 10, 20, 50, 100, 200], 200).
73682

Answer 1

You can easily give more structure to your code:

-module(coins).
-export([coins/2]).
-spec coins([CoinValue::integer()], Goal::integer()) -> Combinations::integer().
coins(_, 0) -> 1;
coins([], _) -> 0;
coins(_, Goal) when Goal < 0 -> 0;
coins([CoinValue|Rest], Goal) ->
 WithCoinValue = coins([H|T], Goal-H),
 WithoutCoinValue = coins(T, Goal),
 WithCoinValue + WithoutCoinValue.

• kharandziuk: Thanks for the spec . About new variables(WithCoinValue, WithoutCoinValue) IMHO, they are spare. But this is a question of taste