Function in prolog with backtracking

Question

The function is

backtracking function f(n,k)

or

f(n, k) = n * k,           if n = k
        = n ∗ f(n−1, k),   if n > k
        = k ∗ f(n,   k−1), if n < k

The Prolog predicate fn/3 assign in order to implement the above function

Can you help me solve the above function? Thank you

Answer 1

You can try with the below predicates.

f(N, K, R):-
    N = K ,
    R is N*K,!.

f(N, K, R):-
    N>K,
    Nx is N-1,
    f(Nx,K,Res),
    R is N*Res.

f(N, K, R):-
    N<K,
    Kx is K-1,
    f(N,Kx,Res),
    R is K * Res.

The R will have the result that you wanted.