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128 lines
3.4 KiB
Python
128 lines
3.4 KiB
Python
"""
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A Trie/Prefix Tree is a kind of search tree used to provide quick lookup
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of words/patterns in a set of words. A basic Trie however has O(n^2) space complexity
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making it impractical in practice. It however provides O(max(search_string, length of
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longest word)) lookup time making it an optimal approach when space is not an issue.
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"""
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class TrieNode:
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def __init__(self):
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self.nodes = dict() # Mapping from char to TrieNode
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self.is_leaf = False
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def insert_many(self, words: [str]):
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"""
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Inserts a list of words into the Trie
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:param words: list of string words
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:return: None
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"""
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for word in words:
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self.insert(word)
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def insert(self, word: str):
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"""
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Inserts a word into the Trie
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:param word: word to be inserted
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:return: None
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"""
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curr = self
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for char in word:
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if char not in curr.nodes:
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curr.nodes[char] = TrieNode()
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curr = curr.nodes[char]
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curr.is_leaf = True
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def find(self, word: str) -> bool:
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"""
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Tries to find word in a Trie
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:param word: word to look for
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:return: Returns True if word is found, False otherwise
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"""
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curr = self
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for char in word:
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if char not in curr.nodes:
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return False
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curr = curr.nodes[char]
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return curr.is_leaf
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def delete(self, word: str):
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"""
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Deletes a word in a Trie
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:param word: word to delete
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:return: None
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"""
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def _delete(curr: TrieNode, word: str, index: int):
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if index == len(word):
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# If word does not exist
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if not curr.is_leaf:
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return False
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curr.is_leaf = False
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return len(curr.nodes) == 0
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char = word[index]
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char_node = curr.nodes.get(char)
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# If char not in current trie node
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if not char_node:
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return False
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# Flag to check if node can be deleted
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delete_curr = _delete(char_node, word, index + 1)
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if delete_curr:
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del curr.nodes[char]
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return len(curr.nodes) == 0
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return delete_curr
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_delete(self, word, 0)
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def print_words(node: TrieNode, word: str):
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"""
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Prints all the words in a Trie
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:param node: root node of Trie
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:param word: Word variable should be empty at start
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:return: None
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"""
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if node.is_leaf:
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print(word, end=" ")
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for key, value in node.nodes.items():
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print_words(value, word + key)
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def test_trie():
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words = "banana bananas bandana band apple all beast".split()
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root = TrieNode()
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root.insert_many(words)
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# print_words(root, "")
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assert all(root.find(word) for word in words)
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assert root.find("banana")
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assert not root.find("bandanas")
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assert not root.find("apps")
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assert root.find("apple")
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assert root.find("all")
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root.delete("all")
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assert not root.find("all")
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root.delete("banana")
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assert not root.find("banana")
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assert root.find("bananas")
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return True
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def print_results(msg: str, passes: bool) -> None:
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print(str(msg), "works!" if passes else "doesn't work :(")
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def pytests():
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assert test_trie()
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def main():
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"""
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>>> pytests()
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"""
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print_results("Testing trie functionality", test_trie())
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if __name__ == "__main__":
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main()
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