Python/data_structures/Trie/Trie.py
2018-01-20 12:35:12 +01:00

76 lines
2.2 KiB
Python

"""
A Trie/Prefix Tree is a kind of search tree used to provide quick lookup
of words/patterns in a set of words. A basic Trie however has O(n^2) space complexity
making it impractical in practice. It however provides O(max(search_string, length of longest word)) lookup
time making it an optimal approach when space is not an issue.
"""
class TrieNode:
def __init__(self):
self.nodes = dict() # Mapping from char to TrieNode
self.is_leaf = False
def insert_many(self, words: [str]): # noqa: F821 This syntax is Python 3 only
"""
Inserts a list of words into the Trie
:param words: list of string words
:return: None
"""
for word in words:
self.insert(word)
def insert(self, word: str): # noqa: F821 This syntax is Python 3 only
"""
Inserts a word into the Trie
:param word: word to be inserted
:return: None
"""
curr = self
for char in word:
if char not in curr.nodes:
curr.nodes[char] = TrieNode()
curr = curr.nodes[char]
curr.is_leaf = True
def find(self, word: str) -> bool: # noqa: F821 This syntax is Python 3 only
"""
Tries to find word in a Trie
:param word: word to look for
:return: Returns True if word is found, False otherwise
"""
curr = self
for char in word:
if char not in curr.nodes:
return False
curr = curr.nodes[char]
return curr.is_leaf
def print_words(node: TrieNode, word: str): # noqa: F821 This syntax is Python 3 only
"""
Prints all the words in a Trie
:param node: root node of Trie
:param word: Word variable should be empty at start
:return: None
"""
if node.is_leaf:
print(word, end=' ')
for key, value in node.nodes.items():
print_words(value, word + key)
def test():
words = ['banana', 'bananas', 'bandana', 'band', 'apple', 'all', 'beast']
root = TrieNode()
root.insert_many(words)
# print_words(root, '')
assert root.find('banana')
assert not root.find('bandanas')
assert not root.find('apps')
assert root.find('apple')
test()