Implement Trie (Prefix Tree)

Description

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.

Code

class Trie {
    Trie* children[26];
    bool isWord;
public:
    Trie() {
        isWord = false;
        for(int i = 0; i < 26; i++) {
            this->children[i] = nullptr;
        }
    }   
 
    void insert(string word) {
        Trie* cur = this;
        for(char c: word) {
            c -= 'a';
            if(cur->children[c] == nullptr) {
                cur->children[c] = new Trie();
            }
            cur = cur->children[c];
        }
        cur->isWord = true;
    }
 
    bool search(string word) {
        Trie* cur = this;
        for(char c: word) {
            c -= 'a';
            if(cur->children[c] == nullptr) return false;
            cur = cur->children[c];
        }
        return cur->isWord;
    }
    
    bool startsWith(string prefix) {
        Trie* cur = this;
        for(char c: prefix) {
            c -= 'a';
            if(cur->children[c] == nullptr) return false;
            cur = cur->children[c];
        }
        return true;
    }
};
 
/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */

Source

• Implement Trie (Prefix Tree) - LeetCode
• Trie 字典樹 – 陪你刷題