Prolog-是否平衡树 [英] Prolog - Balanced tree or not

问题描述

我想编写一个程序，告诉我一棵树是否平衡.在这种情况下，平衡意味着相同的高度或高度差为1.

I want to write a program that tells me if a tree is balanced or not. In this case balanced means same height or a height difference of 1.

这是我到目前为止编写的内容，但是对于1的高度差却不起作用.为什么?

This is what I've written so far but it doesn't work for the height difference of 1. Why?

balanced(l(_)).
balanced(b(B1, B2)):-
    height(B1,H),
    height(B2,H),
    balanced(B1),
    balanced(B2).

balanced(b(B1,B2)):-
    height(B1,H + 1),
    height(B2,H),
    balanced(B1),
    balanced(B2).

balanced(b(B1,B2)):-
    height(B1,H),
    height(B2,H + 1),
    balanced(B1),
    balanced(B2).

推荐答案

H + 1不会被评估为H的值，如果您不告诉Prolog进行算术评估，则不会加一.相反，Prolog用+作为函子，并用H和1作为自变量构建一个术语. (尝试H + 1 =.. L并检查L的值以使自己相信这一事实.)

H + 1 is not evaluated to the value of H plus one if you don't tell Prolog to do arithmetic evaluation; instead, Prolog builds a term with + as the functor and H and 1 as the arguments. (Try H + 1 =.. L and check the value of L to convince yourself of this fact.)

做类似的事情

height(B1, H1),
height(B2, H2),
abs(H1 - H2) =< 1.

=<将执行算术评估.

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