Trie implementation (#111)

* Started Trie implementation.

* Basic definition of Trie in comments at the top of the file
* Defined Trie class and method signatures.

* * Renamed method signatures to match formal definitions

* Finished Simple Trie implementation and added test functions
* Finished function to insert a word into Trie
* Finished function to find a word in the Trie
* Added Test functions with Assertions

* Updated test function to read from the Dictionary.txt file in repository

* * No longer using $ to mark end of word
* No longer reading from file but instead provided simple sample input for easier testing

* Deleting empty __init__.py file

data_structures/Trie/Trie.py

@@ -0,0 +1,75 @@
+"""
+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]):
+        """
+        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
+        """
+        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:
+        """
+        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):
+    """
+    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()