部分订单排序？

本文介绍了部分订单排序？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

说，我们有一些项目，每个项目都定义了一些部分排序规则，例如：

Say, we have some items, and each defines some partial sorting rules, like this:

我是 A ，我想成为 B

我是 C ，我想在 A 之后但在 D 之前p>

I'm C and I want to be after A but before D

因此我们有 A，B，C，D 项，其规则如下：

So we have items A,B,C,D with these rules:

• A> B
• C< A ， C> D
• 没什么！因此， B 和 D 在排序时没有首选项，并且被认为是相等的。

• A>B
• C<A, C>D
• nothing else! So, B and D have no 'preferences' in ordering and are considered equal.

如您所见，传递关系规则在这里不起作用。但是，如果 A> B 仍表示 B< A 。因此，可能会有多种排序结果：

As you see, transitive relation rules are not working here. However, if A>B it still means that B<A. So, there can be multiple possible results of sorting:

ABCD

ACDB

ACBD

ABCD

A B C D

A C D B

A C B D

A B C D

如何实现排序算法

原因：存在多个可加载模块，其中一些模块依赖其他方式。每个模块都可以声明相对于其他模块的简单规则：

The reason: there're multiple loadable modules, and some of them 'depend' on others in a way. Each module can declare simple rules, relative to other modules:

在模块A之前加载我

Load me before module A

在模块B之后加载我

在模块A之前加载我但在模块B之后

Load me before module A but after module B

现在我需要以某种方式实现此排序。：）

now I need to implement this ordering somehow.. :)

答案：代码作者：帕迪·麦卡锡（MIT）

Answer: code by Paddy McCarthy (MIT)

## {{{ code.activestate/recipes/577413/ (r1) try: from functools import reduce except: pass data = { 'des_system_lib': set('std synopsys std_cell_lib des_system_lib dw02 dw01 ramlib ieee'.split()), 'dw01': set('ieee dw01 dware gtech'.split()), 'dw02': set('ieee dw02 dware'.split()), 'dw03': set('std synopsys dware dw03 dw02 dw01 ieee gtech'.split()), 'dw04': set('dw04 ieee dw01 dware gtech'.split()), 'dw05': set('dw05 ieee dware'.split()), 'dw06': set('dw06 ieee dware'.split()), 'dw07': set('ieee dware'.split()), 'dware': set('ieee dware'.split()), 'gtech': set('ieee gtech'.split()), 'ramlib': set('std ieee'.split()), 'std_cell_lib': set('ieee std_cell_lib'.split()), 'synopsys': set(), } def toposort2(data): for k, v in data.items(): v.discard(k) # Ignore self dependencies extra_items_in_deps = reduce(set.union, data.values()) - set(data.keys()) data.update({item:set() for item in extra_items_in_deps}) while True: ordered = set(item for item,dep in data.items() if not dep) if not ordered: break yield ' '.join(sorted(ordered)) data = {item: (dep - ordered) for item,dep in data.items() if item not in ordered} assert not data, "A cyclic dependency exists amongst %r" % data print ('\n'.join( toposort2(data) )) ## end of code.activestate/recipes/577413/ }}}

推荐答案

您将要构建依赖图（这只是有向图的一种），然后按照按拓扑排序排序。自从我参加组合类课程以来已经有一段时间了，因此Wikipedia文章可能比我的拓扑排序算法更有用。我希望给您适当的术语会有所帮助。 ：）

You'll want to construct a dependency graph (which is just a flavor of directed graph), and then follow a topologically sorted ordering. It's been a while since I took a combinatorics class, so the Wikipedia article will probably be more helpful than I am for a topological sort algorithm. I'm hoping giving you the proper terminology is helpful. :)

就构造图而言，基本上只需要让每个模块带有该模块的依赖关系列表即可。

As far as constructing the graph, you'll basically just need to have each module with a list of that module's dependencies.

您只需要稍微改写一下规则即可……我是C，我想成为A之后但D之前，表示为 C取决于A以及 D取决于C，因此所有内容都沿标准方向流动。

You'll just need to rephrase your rules a bit... "I'm C and I want to be after A but before D" would be expressed as "C depends on A" as well as "D depends on C", such that everything is flowing in a standard direction.