trie即字首樹或字典樹，利用字串公共字首降低搜尋時間。速度為o(k),k為輸入的字串長度。
1.採用defaultdict建立trie
from collections import defaultdictfrom 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.採用dictionary結構
#定義trie結構體
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 # 判斷單詞是否是完整的存在在trie樹中
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:
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):
return words
node = self.root
for letter in prefix:
node = node.data.get(letter)
return _get_key(prefix, node)
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