# [leetcode] 208. Implement Trie (Prefix Tree) _ Algorithm Problem Solve for python

## 1. Problem

208. Implement Trie (Prefix Tree)

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.

## 2. Solution

I solved this problem like this.

• Using dictionary, make trie.
class Trie:

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

def insert(self, word: str) -> None:
sub_trie = self.trie
for x in word:
if x not in sub_trie:
sub_trie[x] = {}
sub_trie = sub_trie[x]
sub_trie['exist'] = True

def search(self, word: str) -> bool:
sub_trie = self.trie
for x in word:
if x not in sub_trie:
return False
sub_trie = sub_trie[x]
if 'exist' in sub_trie:
return True
return False

def startsWith(self, prefix: str) -> bool:
sub_trie = self.trie
for x in prefix:
if x not in sub_trie:
return False
sub_trie = sub_trie[x]

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)