特定のマスを特定の歩数目で踏んで迷路を抜けるパズル | Codetter（こーどったー）

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append( [], List, List ).
append( [Head|Tail], List, [Head|TailR] ) :- append(Tail, List, TailR).
at( [Head|Tail], (0, Y), Val ) :- at(Head, Y, Val).
at( [Head|Tail], (X, Y), Val ) :- X > 0, X1 is X - 1, at( Tail, (X1, Y), Val ).
at( [Head|Tail], 0, Head ).
at( [Head|Tail], Idx, Val ) :- number(Idx), Idx > 0, Idx1 is Idx - 1, at( Tail, Idx1, Val ).    
    ?- at( [[1,2,3],[4,5],[6,7]], (0,2), 3 ).
% ルール
walk_maze(Q, A) :-
    Q = A,
    length(Q, M), Q = [H|_],
    length(H, N),
    walk_maze( Q, A, (M, N), (0, 0), 1 ).   % 左上を入口として入る
    
walk_maze( _, _, (M, N),      _, StepEnd ) :- StepEnd is M * N.
walk_maze( Q, A, (M, N), (X, Y), Step ) :-
%   number(M), number(N), number(X), number(Y), number(Step),
    0 =< X, X < M, 0 =< Y, Y < N,
    at( Q, (X, Y), Step ),
    StepNext is Step + 1,
    (   % 次の一歩
        X1 is X - 1, walk_maze( Q, A, (M, N), (X1, Y), StepNext );
        Y1 is Y - 1, walk_maze( Q, A, (M, N), (X, Y1), StepNext );
        X2 is X + 1, walk_maze( Q, A, (M, N), (X2, Y), StepNext );
        Y2 is Y + 1, walk_maze( Q, A, (M, N), (X, Y2), StepNext )
    ).
    
% 例題
    ?- walk_maze( [
        [ 1, _, _, _, _, 36 ],
        [ _, _, _, _, _, _ ],
        [ _, _, _, _, _, _ ],
        [ _, 9, _,27, _, _ ],
        [ _,18, _, _, _, _ ],
        [ _, _, _, _, _, _ ] ], Answer ).
/*
Answer = [
    [  1,  2,  3,  4, 35, 36 ],
    [ 12, 11,  6,  5, 34, 33 ],
    [ 13, 10,  7, 28, 29, 32 ],
    [ 14,  9,  8, 27, 30, 31 ],
    [ 15, 18, 19, 26, 25, 24 ],
    [ 16, 17, 20, 21, 22, 23 ]
]
*/
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