implement_trie_prefix_tree.py

"""
A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.

Implement the Trie class:

Trie() Initializes the trie object.
void insert(String word) Inserts the string word into the trie.
boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.
 

Example 1:

Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output
[null, null, true, false, true, null, true]

Explanation
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple");   // return True
trie.search("app");     // return False
trie.startsWith("app"); // return True
trie.insert("app");
trie.search("app");     // return True
 

Constraints:

1 <= word.length, prefix.length <= 2000
word and prefix consist only of lowercase English letters.
At most 3 * 104 calls in total will be made to insert, search, and startsWith.

"""

class Trie:

    def __init__(self):
        self.trie = {}

    def insert(self, word: str) -> None:
        t = self.trie
		# The idea is to insert words in a linked fashion. For example "cars" will be inserted as
		# {'c':{'a':{'r':{'s':{}}}}
        for w in word:
          if w not in t:
            t[w] = {}
          t = t[w]
		# Another key named "end" will distinguish that the word  "cars" actually exists
		# Without the end key it simply means that the traversed part is just prefix
        t["end"] = True 

    def search(self, word: str) -> bool:
        t = self.trie
		# Traverse through the word
        for w in word:
          if w in t:
            t = t[w]
          else:
            return False
		# As the end key denotes the existence of the word
        return "end" in t

    def startsWith(self, prefix: str) -> bool:
        t = self.trie
		# Traverse through the word
        for w in prefix:
          if w in t:
            t = t[w]
          else:
            return False
		# Here it is okay to find whether we had traversed the entire prefix or not
        return True
        


# Your Trie object will be instantiated and called as such:
# obj = Trie()
# obj.insert(word)
# param_2 = obj.search(word)
# param_3 = obj.startsWith(prefix)