LeetCode-in-All

208. Implement Trie (Prefix Tree)

Medium

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.

Solution

class TrieNode:
    # Initialize your data structure here.
    def __init__(self):
        self.children = [None] * 26
        self.isWord = False

class Trie:
    def __init__(self):
        self.root = TrieNode()
        self.startWith = False

    # Inserts a word into the trie.
    def insert(self, word):
        self._insert(word, self.root, 0)

    def _insert(self, word, root, idx):
        if idx == len(word):
            root.isWord = True
            return
        index = ord(word[idx]) - ord('a')
        if root.children[index] is None:
            root.children[index] = TrieNode()
        self._insert(word, root.children[index], idx + 1)

    # Returns if the word is in the trie.
    def search(self, word):
        return self._search(word, self.root, 0)

    def _search(self, word, root, idx):
        if idx == len(word):
            self.startWith = True
            return root.isWord
        index = ord(word[idx]) - ord('a')
        if root.children[index] is None:
            self.startWith = False
            return False
        return self._search(word, root.children[index], idx + 1)

    # Returns if there is any word in the trie
    # that starts with the given prefix.
    def startsWith(self, prefix):
        self.search(prefix)
        return self.startWith

# 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)

This site is open source. Improve this page.