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208. Implement Trie (Prefix Tree)

문제 링크

https://leetcode.com/problems/implement-trie-prefix-tree/description/

문제 설명

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.

제한 사항

  • 1 <= word.length, prefix.length <= 2000
  • word and prefix consist only of lowercase English letters.
  • At most 3 * 10^4 calls in total will be made to insert, search, and startsWith.

입출력 예 #1

  1. Input : [“Trie”, “insert”, “search”, “search”, “startsWith”, “insert”, “search”] [[], [“apple”], [“apple”], [“app”], [“app”], [“app”], [“app”]]
  2. Output : [null, null, true, false, true, null, true]
  3. 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

문제 풀이

search는 해당 단어가 있는지 여부를 확인하기 위해 마지막 문자의 값을 True로 해주고, startswith는 search와 동일하나 문자열의 문자가 있는지를 순회하며 확인한다.

# 트라이의 노드
class TrieNode:
    def __init__(self):
        self.word = False
        self.children = collections.defaultdict(TrieNode)

class Trie:

    def __init__(self):
        self.root = TrieNode()

    # 단어 삽입
    def insert(self, word: str) -> None:
        node = self.root
        for char in word:
            node = node.children[char]
        node.word = True

    # 단어 존재 여부 판별
    def search(self, word: str) -> bool:
        node = self.root
        for char in word:
            if char not in node.children:
                return False
            node = node.children[char]
        
        return node.word

    # 문자열로 시작 단어 존재 여부 판별
    def startsWith(self, prefix: str) -> bool:
        node = self.root
        for char in prefix:
            if char not in node.children:
                return False
            node = node.children[char]
        
        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)

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