Python容错的前缀树怎么实现中文纠错

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介绍

本文使用 Python 实现了前缀树，并且支持编辑距离容错的查询。文中的前缀树只存储了三个分词，格式为 (分词字符串,频率) ，如：("中海晋西园", 2)、("中海西园", 24)、("中南海", 4)，可以换成自己的文件进行数据的替换。在查询的时候要指定一个字符串和最大的容错编辑距离。

实现

class Word:    def __init__(self, word, freq):        self.word = word        self.freq = freqclass Trie:    def __init__(self):        self.root = LetterNode("")        self.START = 3    def insert(self, word, freq):        self.root.insert(word, freq, 0)    def findAll(self, query, maxDistance):        suggestions = self.root.recommend(query, maxDistance, self.START)        return sorted(set(suggestions), key=lambda x: x.freq)class LetterNode:    def __init__(self, char):        self.REMOVE = -1        self.ADD = 1        self.SAME = 0        self.CHANGE = 2        self.START = 3        self.pointers = []        self.char = char        self.word = None    def charIs(self, c):        return self.char == c    def insert(self, word, freq, depth):        if " " in word:            word = [i for i in word.split(" ")]        if depth < len(word):            c = word[depth].lower()            for next in self.pointers:                if next.charIs(c):                    return next.insert(word, freq, depth + 1)            nextNode = LetterNode(c)            self.pointers.append(nextNode)            return nextNode.insert(word, freq, depth + 1)        else:            self.word = Word(word, freq)    def recommend(self, query, movesLeft, lastAction):        suggestions = []        length = len(query)        if length >= 0 and movesLeft - length >= 0 and self.word:            suggestions.append(self.word)        if movesLeft == 0 and length > 0:            for next in self.pointers:                if next.charIs(query[0]):                    suggestions += next.recommend(query[1:], movesLeft, self.SAME)                    break        elif movesLeft > 0:            for next in self.pointers:                if length > 0:                    if next.charIs(query[0]):                        suggestions += next.recommend(query[1:], movesLeft, self.SAME)                    else:                        suggestions += next.recommend(query[1:], movesLeft - 1, self.CHANGE)                        if lastAction != self.CHANGE and lastAction != self.REMOVE:                            suggestions += next.recommend(query, movesLeft - 1, self.ADD)                        if lastAction != self.ADD and lastAction != self.CHANGE:                            if length > 1 and next.charIs(query[1]):                                suggestions += next.recommend(query[2:], movesLeft - 1, self.REMOVE)                            elif length > 2 and next.charIs(query[2]) and movesLeft == 2:                                suggestions += next.recommend(query[3:], movesLeft - 2, self.REMOVE)                else:                    if lastAction != self.CHANGE and lastAction != self.REMOVE:                        suggestions += next.recommend(query, movesLeft - 1, self.ADD)        return suggestionsdef buildTrieFromFile():    trie = Trie()    rows = [("中海晋西园", 2),("中海西园", 24),("中南海", 4)]    for row in rows:        trie.insert(row[0], int(row[1]))    return triedef suggestor(trie, s, maxDistance):    if " " in s:        s = [x for x in s.split(" ")]    suggestions = trie.findAll(s, maxDistance)    return [str(x.word) for x in suggestions]if __name__ == "__main__":    trie = buildTrieFromFile()    r = suggestor(trie, "中海晋西园", 1)    print(r)

分析

结果打印：
["中海晋西园", "中海西园"]

可以看出"中海晋西园"是和输入完全相同的字符串，编辑距离为 0 ，所以符合最大编辑距离为 1 的要求，直接返回。

"中海西园"是"中海晋西园"去掉"晋"字之后的结果，编辑距离为 1， 所以符合最大编辑距离为 1 的要求，直接返回。

另外，"中南海"和"中海晋西园"的编辑距离为 4 ，不符合最大编辑距离为 1 的要求，所以结果中没有出现。

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