Stamps II X68780

We want to send a postcard by mail. We need to stamp worth n cents (n≥ 20). Stamps have values 7 and 4 cents. As space is limited we want to know the minimum number of stamps we need to put on the postcard, without losing a cent.

Using the definition

implement a recursive function

computing the mimimum number of necessary worth 7 stamps (stamp7 field) and worth 4 stamps (stamp4 field) for a total worth of n cents (n ≥ 20). For instance, for n = 58, the result fields of min_stamps must be 6 and 4.

Observation In order to complete the recursive case, note that recursive calls will always provide a Stamps tuple with stamp4 field at most 6.

Observation This problem is an example about using tuples in order to define functions computing a result that does not have a default representation as a single value.

Observation You only need to submit the required classes; your main program will be ignored. Strictly obey the type definitions of the statement.