[Leetcode] 0208. Implement Trie

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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.

內容目錄

Python

				
					# insert()
# time complexity: O(l)
# space complexity: O(l)
# search()
# time complexity: O(l)
# space complexity: O(1)
# search prefix()
# time complexity: O(l)
# space complexity: O(1)
class TrieNode:
    def __init__(self, char: str = ""):
        self.char = char
        self.children = {}
        self.isEnd = False


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

    def insert(self, word: str):
        node = self.root
        for c in word:
            if c in node.children:
                node = node.children[c]
            else:
                newNode = TrieNode()
                node.children[c] = newNode
                node = newNode
        node.isEnd = True

    def search(self, word: str):
        node = self.root
        for c in word:
            if c not in node.children:
                return False    
            node = node.children[c]
        return node.isEnd
    
    def startsWith(self, prefix: str):
        node = self.root
        for c in prefix:
            if c not in node.children:
                return False
            node = node.children[c]
        return True


# Your Trie object will be instantiated and called as such:
trie = Trie()
trie.insert("apple")
print(trie.search("apple"))
print(trie.search("app"))
print(trie.startsWith("app"))
trie.insert("app")
print(trie.search("app"))

Python

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