Python3创建一个trie的两种方法

Trie即前缀树或字典树，利用字符串公共前缀降低搜索时间。速度为O(k),k为输入的字符串长度。

1.采用defaultdict创建trie

from collections import defaultdict
from functools import reduce
TrieNode = lambda: defaultdict(TrieNode)
class Trie:
    def __init__(self):
        self.trie = TrieNode()
    def insert(self, word):
        reduce(dict.__getitem__, word, self.trie)['end'] = True
    def search(self, word):
        return reduce(lambda d,k: d[k] if k in d else TrieNode(), word, self.trie).get('end', False)
    def startsWith(self, word):
        return bool(reduce(lambda d,k: d[k] if k in d else TrieNode(), word, self.trie).keys())

 2.采用dictionary结构

#定义trie结构体

class TrieNode(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.data = {}
        self.is_word = False
 
class Trie(object):
    def __init__(self):
        self.root = TrieNode()
 
    def insert(self, word):
        """
        Inserts a word into the trie.
        :type word: str
        :rtype: void
        """
        node = self.root
        for letter in word:
            child = node.data.get(letter)
            if not child:
                node.data[letter] = TrieNode()
            node = node.data[letter]
        node.is_word = True
 
    def search(self, word):
        """
        Returns if the word is in the trie.
        :type word: str
        :rtype: bool
        """
        node = self.root
        for letter in word:
            node = node.data.get(letter)
            if not node:
                return False
        return node.is_word  # 判断单词是否是完整的存在在trie树中
 
    def starts_with(self, prefix):
        """
        Returns if there is any word in the trie
        that starts with the given prefix.
        :type prefix: str
        :rtype: bool
        """
        node = self.root
        for letter in prefix:
            node = node.data.get(letter)
            if not node:
                return False
        return True
 
    def get_start(self, prefix):
        """
        Returns words started with prefix
        :param prefix:
        :return: words (list)
        """
        def _get_key(pre, pre_node):
            words_list = []
            if pre_node.is_word:
                words_list.append(pre)
            for x in pre_node.data.keys():
                words_list.extend(_get_key(pre + str(x), pre_node.data.get(x)))
            return words_list
 
        words = []
        if not self.starts_with(prefix):
            return words
        if self.search(prefix):
            words.append(prefix)
            return words
        node = self.root
        for letter in prefix:
            node = node.data.get(letter)
        return _get_key(prefix, node)