RabbitFarm

The examples used here are from the weekly challenge problem statement and demonstrate the working solution.

Part 1

You are given two arrays of integers. Write a script to find out the missing members in each other arrays.

Solution

missing(L, E, Member):-
    (member(E, L), Member = nil);
    (\+ member(E, L), Member = E).
missing_members([List1, List2], [Missing1, Missing2]):-
    maplist(missing(List2), List1, Missing1Nil),
    delete(Missing1Nil, nil, Missing1),
    maplist(missing(List1), List2, Missing2Nil),
    delete(Missing2Nil, nil, Missing2). 

Sample Run

% gprolog --consult-file prolog/ch-1.p
| ?- missing_members([[1, 2, 3], [2, 4, 6]] ,Missing).

Missing = [[1,3],[4,6]] ? 

yes
| ?- missing_members([[1, 2, 3, 3], [1, 1, 2, 2]] ,Missing).

Missing = [[3,3],[]] ? 

yes
| ?- missing_members([[1, 2, 3, 3], [1, 1, 2, 2]], Missing), maplist(sort, Missing, MissingNoDuplicates). 

Missing = [[3,3],[]]
MissingNoDuplicates = [[3],[]] ? 

yes
| ?- 

Notes

missing/3 is used in a maplist/3 to determine which elements are missing from an array. If they are not missing a nil is set for it. By deleting the nil elements all that remain are the ones that are missing. This solution doesn't itself remove duplicate missing elements that are identified. That said, as you can see in the example above that can be added, say, using sort/2.

Part 2

You are given n x n binary matrix. Write a script to flip the given matrix as below.

Solution

flip(B, F):-
    F is \ B /\ 1.
flip_matrix([], []).    
flip_matrix([Row|Matrix], [RowFlipped|MatrixFlipped]):-
    reverse(Row, RowReversed),
    maplist(flip, RowReversed, RowFlipped),
    flip_matrix(Matrix, MatrixFlipped).

Sample Run

% gprolog --consult-file prolog/ch-2.p 
| ?- flip_matrix([[1, 1, 0], [1, 0, 1], [0, 0, 0]], FlippedMatrix).

FlippedMatrix = [[1,0,0],[0,1,0],[1,1,1]]

yes
| ?- flip_matrix([[1, 1, 0, 0], [1, 0, 0, 1], [0, 1, 1, 1], [1, 0, 1, 0]], FlippedMatrix).

FlippedMatrix = [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]

yes
| ?- 

Notes

For the given matrix we need only recursively consider each row, reverse it, do the necessary bit flips, and then assemble the newly flipped rows into the completed Flipped Matrix.

References

Challenge 242