了解序言中quicksort的运行轨迹 [英] understand the running trace of quicksort in prolog

问题描述

我有以下用于快速排序的序言代码:

I have the following prolog code for quicksort:

gt(X,Y):- X @> Y.
conc([], List, List).
conc([Head|Tail], List1, [Head|List2]):- conc(Tail, List1, List2).

quicksort([], []).
quicksort([X|Tail], Sorted):-
    split(X,Tail,Small,Big),
    quicksort(Small,SortedSmall),
    quicksort(Big, SortedBig),
    conc(SortedSmall, [X|SortedBig], Sorted).

split(X,[],[],[]).
split(X,[Y|Tail],[Y|Small],Big):-
    gt(X,Y),
    !,
    split(X,Tail,Small, Big).

split(X,[Y|Tail],Small,[Y|Big]):-
    split(X,Tail,Small,Big).

例如，数组为[3,2,4,1,5]. quicksort([3,2,4,1,5]，已排序).我需要了解程序的运行轨迹.我几乎做到了，但有一点我没有:(这只是跟踪的一部分):

The array for example is [3,2,4,1,5]. quicksort([3,2,4,1,5], Sorted). I need to understand the running trace of the program. I almost do but there is one point that I don't: (this is just a part of the trace):

Redo: (11) split(3, [5], _G3785, _G3782) ? creep
Call: (12) split(3, [], _G3785, _G3788) ? creep
Exit: (12) split(3, [], [], []) ? creep
Exit: (11) split(3, [5], [], [5]) ? creep
Exit: (10) split(3, [1, 5], [1], [5]) ? creep
Exit: (9) split(3, [4, 1, 5], [1], [4, 5]) ? creep
Exit: (8) split(3, [2, 4, 1, 5], [2, 1], [4, 5]) ? creep

我们为什么要退出:(11)split(3，[5]，[]，[5])?在第11行蠕变5从何而来? 有人可以帮我！我真的很感激.

Why do we have Exit: (11) split(3, [5], [], [5]) ? creep at the line 11, where does 5 come from? Someone could help me please!! I'd really appreciate that.

推荐答案

在对函数split的规则编号2进行比较之后，应该进行剪切:

There should be a cut after comparing at the rule number 2 of function split:

split(X,[Y|Tail],[Y|Small],Big):-
gt(X,Y), 
!,
split(X,Tail,Small, Big).

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