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)