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

use std::collections::HashMap;

struct Trie {
    tree: HashMap<char, Vec<String>>
}

/**
  * `&self` means the method takes an immutable reference
  * If you need a mutable reference, change it to `&mut self` instead.
 */
impl Trie {

    fn new() -> Self {
        Trie{tree:HashMap::new()}
    }

    fn insert(&mut self, word: String) {
        self.tree.entry(word.chars().next().unwrap()).or_default().push(word);
    }

    fn search(&self, word: String) -> bool {
        if let Some(vals) = self.tree.get(&word.chars().next().unwrap()) {
            return vals.contains(&word)
        }
        false
    }

    fn starts_with(&self, prefix: String) -> bool {
        if let Some(vals) = self.tree.get(&prefix.chars().next().unwrap()) {
            return vals.iter().any(|word| word.starts_with(&prefix))
        }
        false
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * let obj = Trie::new();
 * obj.insert(word);
 * let ret_2: bool = obj.search(word);
 * let ret_3: bool = obj.starts_with(prefix);
 */

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