Trie implementation

data_structures/Trie/Trie.py

@@ -0,0 +1,81 @@
+"""
+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.
+
+This implementation assumes the character $ is not in any of the words. This character is used in the implementation
+to mark the end of a word.
+"""
+
+
+class TrieNode:
+    def __init__(self):
+        self.nodes = dict()  # Mapping from char to TrieNode
+
+    def insert_many(self, words: [str]):
+        """
+        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):
+        """
+        Inserts a word into the Trie
+        :param word: word to be inserted
+        :return: None
+        """
+        word += '$'
+        curr = self
+        for char in word:
+            if char not in curr.nodes:
+                curr.nodes[char] = TrieNode()
+            curr = curr.nodes[char]
+
+    def find(self, word: str) -> bool:
+        """
+        Tries to find word in a Trie
+        :param word: word to look for
+        :return: Returns True if word is found, False otherwise
+        """
+        word += '$'
+        curr = self
+        for char in word:
+            if char not in curr.nodes:
+                return False
+            curr = curr.nodes[char]
+        return True
+
+
+def print_words(node: TrieNode, word: str):
+    """
+    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 '$' in node.nodes:
+        print(word, end=' ')
+
+    for key, value in node.nodes.items():
+        print_words(value, word + key)
+
+
+def test():
+    words = []
+    # Load words from text file into Trie
+    with open("../../other/Dictionary.txt", "r") as ins:
+        for line in ins:
+            words.append(line.strip().lower())
+    root = TrieNode()
+    root.insert_many(words)
+    # print_words(root, '')
+    assert root.find('bananas')
+    assert not root.find('bandanas')
+    assert not root.find('apps')
+    assert root.find('apple')
+
+# test()