您可以在此处使用 unification 代替 is/2(通常用于计算表达式)。
例如,假设第二个塔是空的,我们可以定义从第一个塔到第二个塔的移动:
changeState((s([A|T1],[], T3)), s(T1, [A], T3)).
或者我们可以将一个元素移动到第二个非空的塔,假设堆栈的顶部是一个更大的元素:
changeState(s([A|T1], [B|T2], T3), s(T1, [A,B|T2], T3)) :-
A < B.
以上将产生总共 12 条规则:3 个来源,乘以 2 个目的地乘以 2 个可能性(空目的地与非空目的地)。这不是很优雅。我们可以构造一个辅助谓词来检查目标堆栈是否有效,使用:
valid_stack([], _).
valid_stack([H|_], X) :-
X < H.
那么我们可以将上面的两条规则压缩成:
changeState((s([A|T1], T2, T3)), s(T1, [A|T2], T3)) :-
valid_stack(T2, A).
这将因此产生六个规则:三个来源和两个目的地。
因此我们不再需要验证移动,因为如果changeState 成功,那么建议移动是可能的假设原始状态是有效的。
但这不是完整的解决方案(我将其余部分留作练习)。您将需要一种机制来枚举可能的移动,并确保您不会陷入循环(例如在两座塔之间不断移动圆盘)。
使用traverse/3 谓词后,我们获得了一个移动到目标的列表:
?- traverse(s([1,2,3,4,5,6], [], []), S, [s([1,2,3,4,5,6], [], [])]).
S = [s([1, 2, 3, 4, 5, 6], [], []), s([2, 3, 4, 5, 6], [1], []), s([3, 4, 5, 6], [1], [2]), s([1, 3, 4, 5|...], [], [2]), s([3, 4, 5|...], [], [1, 2]), s([4, 5|...], [3], [1, 2]), s([1|...], [3], [2]), s([...|...], [...|...], [...]), s(..., ..., ...)|...] [write]
S = [s([1, 2, 3, 4, 5, 6], [], []), s([2, 3, 4, 5, 6], [1], []), s([3, 4, 5, 6], [1], [2]), s([1, 3, 4, 5, 6], [], [2]), s([3, 4, 5, 6], [], [1, 2]), s([4, 5, 6], [3], [1, 2]), s([1, 4, 5, 6], [3], [2]), s([4, 5, 6], [1, 3], [2]), s([2, 4, 5, 6], [1, 3], []), s([1, 2, 4, 5, 6], [3], []), s([2, 4, 5, 6], [3], [1]), s([4, 5, 6], [2, 3], [1]), s([1, 4, 5, 6], [2, 3], []), s([4, 5, 6], [1, 2, 3], []), s([5, 6], [1, 2, 3], [4]), s([1, 5, 6], [2, 3], [4]), s([5, 6], [2, 3], [1, 4]), s([2, 5, 6], [3], [1, 4]), s([1, 2, 5, 6], [3], [4]), s([2, 5, 6], [1, 3], [4]), s([5, 6], [1, 3], [2, 4]), s([1, 5, 6], [3], [2, 4]), s([5, 6], [3], [1, 2, 4]), s([3, 5, 6], [], [1, 2, 4]), s([1, 3, 5, 6], [], [2, 4]), s([3, 5, 6], [1], [2, 4]), s([2, 3, 5, 6], [1], [4]), s([1, 2, 3, 5, 6], [], [4]), s([2, 3, 5, 6], [], [1, 4]), s([3, 5, 6], [2], [1, 4]), s([1, 3, 5, 6], [2], [4]), s([3, 5, 6], [1, 2], [4]), s([5, 6], [1, 2], [3, 4]), s([1, 5, 6], [2], [3, 4]), s([5, 6], [2], [1, 3, 4]), s([2, 5, 6], [], [1, 3, 4]), s([1, 2, 5, 6], [], [3, 4]), s([2, 5, 6], [1], [3, 4]), s([5, 6], [1], [2, 3, 4]), s([1, 5, 6], [], [2, 3, 4]), s([5, 6], [], [1, 2, 3, 4]), s([6], [5], [1, 2, 3, 4]), s([1, 6], [5], [2, 3, 4]), s([6], [1, 5], [2, 3, 4]), s([2, 6], [1, 5], [3, 4]), s([1, 2, 6], [5], [3, 4]), s([2, 6], [5], [1, 3, 4]), s([6], [2, 5], [1, 3, 4]), s([1, 6], [2, 5], [3, 4]), s([6], [1, 2, 5], [3, 4]), s([3, 6], [1, 2, 5], [4]), s([1, 3, 6], [2, 5], [4]), s([3, 6], [2, 5], [1, 4]), s([2, 3, 6], [5], [1, 4]), s([1, 2, 3, 6], [5], [4]), s([2, 3, 6], [1, 5], [4]), s([3, 6], [1, 5], [2, 4]), s([1, 3, 6], [5], [2, 4]), s([3, 6], [5], [1, 2, 4]), s([6], [3, 5], [1, 2, 4]), s([1, 6], [3, 5], [2, 4]), s([6], [1, 3, 5], [2, 4]), s([2, 6], [1, 3, 5], [4]), s([1, 2, 6], [3, 5], [4]), s([2, 6], [3, 5], [1, 4]), s([6], [2, 3, 5], [1, 4]), s([1, 6], [2, 3, 5], [4]), s([6], [1, 2, 3, 5], [4]), s([4, 6], [1, 2, 3, 5], []), s([1, 4, 6], [2, 3, 5], []), s([4, 6], [2, 3, 5], [1]), s([2, 4, 6], [3, 5], [1]), s([1, 2, 4, 6], [3, 5], []), s([2, 4, 6], [1, 3, 5], []), s([4, 6], [1, 3, 5], [2]), s([1, 4, 6], [3, 5], [2]), s([4, 6], [3, 5], [1, 2]), s([3, 4, 6], [5], [1, 2]), s([1, 3, 4, 6], [5], [2]), s([3, 4, 6], [1, 5], [2]), s([2, 3, 4, 6], [1, 5], []), s([1, 2, 3, 4, 6], [5], []), s([2, 3, 4, 6], [5], [1]), s([3, 4, 6], [2, 5], [1]), s([1, 3, 4, 6], [2, 5], []), s([3, 4, 6], [1, 2, 5], []), s([4, 6], [1, 2, 5], [3]), s([1, 4, 6], [2, 5], [3]), s([4, 6], [2, 5], [1, 3]), s([2, 4, 6], [5], [1, 3]), s([1, 2, 4, 6], [5], [3]), s([2, 4, 6], [1, 5], [3]), s([4, 6], [1, 5], [2, 3]), s([1, 4, 6], [5], [2, 3]), s([4, 6], [5], [1, 2, 3]), s([6], [4, 5], [1, 2, 3]), s([1, 6], [4, 5], [2, 3]), s([6], [1, 4, 5], [2, 3]), s([2, 6], [1, 4, 5], [3]), s([1, 2, 6], [4, 5], [3]), s([2, 6], [4, 5], [1, 3]), s([6], [2, 4, 5], [1, 3]), s([1, 6], [2, 4, 5], [3]), s([6], [1, 2, 4, 5], [3]), s([3, 6], [1, 2, 4, 5], []), s([1, 3, 6], [2, 4, 5], []), s([3, 6], [2, 4, 5], [1]), s([2, 3, 6], [4, 5], [1]), s([1, 2, 3, 6], [4, 5], []), s([2, 3, 6], [1, 4, 5], []), s([3, 6], [1, 4, 5], [2]), s([1, 3, 6], [4, 5], [2]), s([3, 6], [4, 5], [1, 2]), s([6], [3, 4, 5], [1, 2]), s([1, 6], [3, 4, 5], [2]), s([6], [1, 3, 4, 5], [2]), s([2, 6], [1, 3, 4, 5], []), s([1, 2, 6], [3, 4, 5], []), s([2, 6], [3, 4, 5], [1]), s([6], [2, 3, 4, 5], [1]), s([1, 6], [2, 3, 4, 5], []), s([6], [1, 2, 3, 4, 5], []), s([], [1, 2, 3, 4, 5], [6]), s([1], [2, 3, 4, 5], [6]), s([], [2, 3, 4, 5], [1, 6]), s([2], [3, 4, 5], [1, 6]), s([1, 2], [3, 4, 5], [6]), s([2], [1, 3, 4, 5], [6]), s([], [1, 3, 4, 5], [2, 6]), s([1], [3, 4, 5], [2, 6]), s([], [3, 4, 5], [1, 2, 6]), s([3], [4, 5], [1, 2, 6]), s([1, 3], [4, 5], [2, 6]), s([3], [1, 4, 5], [2, 6]), s([2, 3], [1, 4, 5], [6]), s([1, 2, 3], [4, 5], [6]), s([2, 3], [4, 5], [1, 6]), s([3], [2, 4, 5], [1, 6]), s([1, 3], [2, 4, 5], [6]), s([3], [1, 2, 4, 5], [6]), s([], [1, 2, 4, 5], [3, 6]), s([1], [2, 4, 5], [3, 6]), s([], [2, 4, 5], [1, 3, 6]), s([2], [4, 5], [1, 3, 6]), s([1, 2], [4, 5], [3, 6]), s([2], [1, 4, 5], [3, 6]), s([], [1, 4, 5], [2, 3, 6]), s([1], [4, 5], [2, 3, 6]), s([], [4, 5], [1, 2, 3, 6]), s([4], [5], [1, 2, 3, 6]), s([1, 4], [5], [2, 3, 6]), s([4], [1, 5], [2, 3, 6]), s([2, 4], [1, 5], [3, 6]), s([1, 2, 4], [5], [3, 6]), s([2, 4], [5], [1, 3, 6]), s([4], [2, 5], [1, 3, 6]), s([1, 4], [2, 5], [3, 6]), s([4], [1, 2, 5], [3, 6]), s([3, 4], [1, 2, 5], [6]), s([1, 3, 4], [2, 5], [6]), s([3, 4], [2, 5], [1, 6]), s([2, 3, 4], [5], [1, 6]), s([1, 2, 3, 4], [5], [6]), s([2, 3, 4], [1, 5], [6]), s([3, 4], [1, 5], [2, 6]), s([1, 3, 4], [5], [2, 6]), s([3, 4], [5], [1, 2, 6]), s([4], [3, 5], [1, 2, 6]), s([1, 4], [3, 5], [2, 6]), s([4], [1, 3, 5], [2, 6]), s([2, 4], [1, 3, 5], [6]), s([1, 2, 4], [3, 5], [6]), s([2, 4], [3, 5], [1, 6]), s([4], [2, 3, 5], [1, 6]), s([1, 4], [2, 3, 5], [6]), s([4], [1, 2, 3, 5], [6]), s([], [1, 2, 3, 5], [4, 6]), s([1], [2, 3, 5], [4, 6]), s([], [2, 3, 5], [1, 4, 6]), s([2], [3, 5], [1, 4, 6]), s([1, 2], [3, 5], [4, 6]), s([2], [1, 3, 5], [4, 6]), s([], [1, 3, 5], [2, 4, 6]), s([1], [3, 5], [2, 4, 6]), s([], [3, 5], [1, 2, 4, 6]), s([3], [5], [1, 2, 4, 6]), s([1, 3], [5], [2, 4, 6]), s([3], [1, 5], [2, 4, 6]), s([2, 3], [1, 5], [4, 6]), s([1, 2, 3], [5], [4, 6]), s([2, 3], [5], [1, 4, 6]), s([3], [2, 5], [1, 4, 6]), s([1, 3], [2, 5], [4, 6]), s([3], [1, 2, 5], [4, 6]), s([], [1, 2, 5], [3, 4, 6]), s([1], [2, 5], [3, 4, 6]), s([], [2, 5], [1, 3, 4, 6]), s([2], [5], [1, 3, 4, 6]), s([1, 2], [5], [3, 4, 6]), s([2], [1, 5], [3, 4, 6]), s([], [1, 5], [2, 3, 4, 6]), s([1], [5], [2, 3, 4, 6]), s([], [5], [1, 2, 3, 4, 6]), s([5], [], [1, 2, 3, 4, 6]), s([1, 5], [], [2, 3, 4, 6]), s([5], [1], [2, 3, 4, 6]), s([2, 5], [1], [3, 4, 6]), s([1, 2, 5], [], [3, 4, 6]), s([2, 5], [], [1, 3, 4, 6]), s([5], [2], [1, 3, 4, 6]), s([1, 5], [2], [3, 4, 6]), s([5], [1, 2], [3, 4, 6]), s([3, 5], [1, 2], [4, 6]), s([1, 3, 5], [2], [4, 6]), s([3, 5], [2], [1, 4, 6]), s([2, 3, 5], [], [1, 4, 6]), s([1, 2, 3, 5], [], [4, 6]), s([2, 3, 5], [1], [4, 6]), s([3, 5], [1], [2, 4, 6]), s([1, 3, 5], [], [2, 4, 6]), s([3, 5], [], [1, 2, 4, 6]), s([5], [3], [1, 2, 4, 6]), s([1, 5], [3], [2, 4, 6]), s([5], [1, 3], [2, 4, 6]), s([2, 5], [1, 3], [4, 6]), s([1, 2, 5], [3], [4, 6]), s([2, 5], [3], [1, 4, 6]), s([5], [2, 3], [1, 4, 6]), s([1, 5], [2, 3], [4, 6]), s([5], [1, 2, 3], [4, 6]), s([4, 5], [1, 2, 3], [6]), s([1, 4, 5], [2, 3], [6]), s([4, 5], [2, 3], [1, 6]), s([2, 4, 5], [3], [1, 6]), s([1, 2, 4, 5], [3], [6]), s([2, 4, 5], [1, 3], [6]), s([4, 5], [1, 3], [2, 6]), s([1, 4, 5], [3], [2, 6]), s([4, 5], [3], [1, 2, 6]), s([3, 4, 5], [], [1, 2, 6]), s([1, 3, 4, 5], [], [2, 6]), s([3, 4, 5], [1], [2, 6]), s([2, 3, 4, 5], [1], [6]), s([1, 2, 3, 4, 5], [], [6]), s([2, 3, 4, 5], [], [1, 6]), s([3, 4, 5], [2], [1, 6]), s([1, 3, 4, 5], [2], [6]), s([3, 4, 5], [1, 2], [6]), s([4, 5], [1, 2], [3, 6]), s([1, 4, 5], [2], [3, 6]), s([4, 5], [2], [1, 3, 6]), s([2, 4, 5], [], [1, 3, 6]), s([1, 2, 4, 5], [], [3, 6]), s([2, 4, 5], [1], [3, 6]), s([4, 5], [1], [2, 3, 6]), s([1, 4, 5], [], [2, 3, 6]), s([4, 5], [], [1, 2, 3, 6]), s([5], [4], [1, 2, 3, 6]), s([1, 5], [4], [2, 3, 6]), s([5], [1, 4], [2, 3, 6]), s([2, 5], [1, 4], [3, 6]), s([1, 2, 5], [4], [3, 6]), s([2, 5], [4], [1, 3, 6]), s([5], [2, 4], [1, 3, 6]), s([1, 5], [2, 4], [3, 6]), s([5], [1, 2, 4], [3, 6]), s([3, 5], [1, 2, 4], [6]), s([1, 3, 5], [2, 4], [6]), s([3, 5], [2, 4], [1, 6]), s([2, 3, 5], [4], [1, 6]), s([1, 2, 3, 5], [4], [6]), s([2, 3, 5], [1, 4], [6]), s([3, 5], [1, 4], [2, 6]), s([1, 3, 5], [4], [2, 6]), s([3, 5], [4], [1, 2, 6]), s([5], [3, 4], [1, 2, 6]), s([1, 5], [3, 4], [2, 6]), s([5], [1, 3, 4], [2, 6]), s([2, 5], [1, 3, 4], [6]), s([1, 2, 5], [3, 4], [6]), s([2, 5], [3, 4], [1, 6]), s([5], [2, 3, 4], [1, 6]), s([1, 5], [2, 3, 4], [6]), s([5], [1, 2, 3, 4], [6]), s([], [1, 2, 3, 4], [5, 6]), s([1], [2, 3, 4], [5, 6]), s([], [2, 3, 4], [1, 5, 6]), s([2], [3, 4], [1, 5, 6]), s([1, 2], [3, 4], [5, 6]), s([2], [1, 3, 4], [5, 6]), s([], [1, 3, 4], [2, 5, 6]), s([1], [3, 4], [2, 5, 6]), s([], [3, 4], [1, 2, 5, 6]), s([3], [4], [1, 2, 5, 6]), s([1, 3], [4], [2, 5, 6]), s([3], [1, 4], [2, 5, 6]), s([2, 3], [1, 4], [5, 6]), s([1, 2, 3], [4], [5, 6]), s([2, 3], [4], [1, 5, 6]), s([3], [2, 4], [1, 5, 6]), s([1, 3], [2, 4], [5, 6]), s([3], [1, 2, 4], [5, 6]), s([], [1, 2, 4], [3, 5, 6]), s([1], [2, 4], [3, 5, 6]), s([], [2, 4], [1, 3, 5, 6]), s([2], [4], [1, 3, 5, 6]), s([1, 2], [4], [3, 5, 6]), s([2], [1, 4], [3, 5, 6]), s([], [1, 4], [2, 3, 5, 6]), s([1], [4], [2, 3, 5, 6]), s([], [4], [1, 2, 3, 5, 6]), s([4], [], [1, 2, 3, 5, 6]), s([1, 4], [], [2, 3, 5, 6]), s([4], [1], [2, 3, 5, 6]), s([2, 4], [1], [3, 5, 6]), s([1, 2, 4], [], [3, 5, 6]), s([2, 4], [], [1, 3, 5, 6]), s([4], [2], [1, 3, 5, 6]), s([1, 4], [2], [3, 5, 6]), s([4], [1, 2], [3, 5, 6]), s([3, 4], [1, 2], [5, 6]), s([1, 3, 4], [2], [5, 6]), s([3, 4], [2], [1, 5, 6]), s([2, 3, 4], [], [1, 5, 6]), s([1, 2, 3, 4], [], [5, 6]), s([2, 3, 4], [1], [5, 6]), s([3, 4], [1], [2, 5, 6]), s([1, 3, 4], [], [2, 5, 6]), s([3, 4], [], [1, 2, 5, 6]), s([4], [3], [1, 2, 5, 6]), s([1, 4], [3], [2, 5, 6]), s([4], [1, 3], [2, 5, 6]), s([2, 4], [1, 3], [5, 6]), s([1, 2, 4], [3], [5, 6]), s([2, 4], [3], [1, 5, 6]), s([4], [2, 3], [1, 5, 6]), s([1, 4], [2, 3], [5, 6]), s([4], [1, 2, 3], [5, 6]), s([], [1, 2, 3], [4, 5, 6]), s([1], [2, 3], [4, 5, 6]), s([], [2, 3], [1, 4, 5, 6]), s([2], [3], [1, 4, 5, 6]), s([1, 2], [3], [4, 5, 6]), s([2], [1, 3], [4, 5, 6]), s([], [1, 3], [2, 4, 5, 6]), s([1], [3], [2, 4, 5, 6]), s([], [3], [1, 2, 4, 5, 6]), s([3], [], [1, 2, 4, 5, 6]), s([1, 3], [], [2, 4, 5, 6]), s([3], [1], [2, 4, 5, 6]), s([2, 3], [1], [4, 5, 6]), s([1, 2, 3], [], [4, 5, 6]), s([2, 3], [], [1, 4, 5, 6]), s([3], [2], [1, 4, 5, 6]), s([1, 3], [2], [4, 5, 6]), s([3], [1, 2], [4, 5, 6]), s([], [1, 2], [3, 4, 5, 6]), s([1], [2], [3, 4, 5, 6]), s([], [2], [1, 3, 4, 5, 6]), s([2], [], [1, 3, 4, 5, 6]), s([1, 2], [], [3, 4, 5, 6]), s([2], [1], [3, 4, 5, 6]), s([], [1], [2, 3, 4, 5, 6]), s([1], [], [2, 3, 4, 5, 6]), s([], [], [1, 2, 3, 4, 5, 6])]
在 SWI-Prolog 中,您需要点击 W 向交互式 shell 发送 print the full list。