字符串搜索库的结果错误或功能或我的编码错误？

Question

我使用的是thispython库，它实现了Aho-Corasick字符串搜索算法，可以在一个过程中在给定字符串中找到一组模式。输出不是我期望的：

In [4]: import ahocorasick
In [5]: import collections

In [6]: tree = ahocorasick.KeywordTree()

In [7]: ss = "this is the first sentence in this book the first sentence is really the most interesting the first sentence is always first"

In [8]: words = ["first sentence is", "first sentence", "the first sentence", "the first sentence is"]

In [9]: for w in words:
   ...:     tree.add(w)
   ...:

In [10]: tree.make()

In [13]: final = collections.defaultdict(int)

In [15]: for match in tree.findall(ss, allow_overlaps=True):
   ....:     final[ss[match[0]:match[1]]] += 1
   ....:

In [16]: final
{   'the first sentence': 3, 'the first sentence is': 2}

我期望的输出是：

^{pr2}$

我错过什么了吗？我是在大字符串上这样做的，所以后期处理不是我的第一选择。有没有办法得到想要的输出？在

Answer 1

我理解Aho-Corasick算法的方式和我实现它的方式会让我同意您的预期输出。看起来您正在使用的Python库出错了，或者可能有一个标志，您可以告诉它从某个位置开始提供所有匹配项，而不仅仅是从特定位置开始的最长匹配项。在

原始论文http://www.win.tue.nl/~watson/2R080/opdracht/p333-aho-corasick.pdf中的示例支持您的理解。在

Answer 2

我不知道ahocorasick模块，但这些结果似乎令人怀疑。acora模块显示如下：

import acora
import collections

ss = "this is the first sentence in this book "
     "the first sentence is really the most interesting "
     "the first sentence is always first"

words = ["first sentence is", 
         "first sentence",
         "the first sentence",
         "the first sentence is"]

tree = acora.AcoraBuilder(*words).build()

for match in tree.findall(ss):
    result[match] += 1

结果：

^{2}$