208. Implement Trie (Prefix Tree)

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.

class _Trie {
private:
    _Trie* t[26];
    bool endOfWord;

public:
    _Trie () : endOfWord(false) {
        memset(t, 0, sizeof(t));
    }
    
    _Trie* insertIfAbsence(char c) {
        if (t[c-'a'] == NULL) t[c-'a'] = new _Trie();
        return t[c-'a'];
    }
    
    _Trie* get(char c) {
        return t[c-'a'];
    }
    
    void eow() {this->endOfWord = true;}
    
    bool getEow() { return this->endOfWord; }
};

class Trie {
    _Trie* trie;
public:
    /** Initialize your data structure here. */
    Trie() {
        this->trie = new _Trie(); 
    }

    /** Inserts a word into the trie. */
    void insert(string word) {
        _Trie* cur = trie;
        for(int i = 0; i < word.size(); i++) {
            cur = cur->insertIfAbsence(word[i]);
        }
        cur->eow();
    }

    /** Returns if the word is in the trie. */
    bool search(string word) {
        _Trie* cur = trie;
        for(int i = 0; i < word.size() && cur; i++) {
            cur = cur->get(word[i]);
        }
        return cur && cur->getEow();
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        _Trie* cur = trie;
        for(int i = 0; i < prefix.size() && cur; i++) {
            cur = cur->get(prefix[i]);
        }
        return cur;
    }
};

/**
 * 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);
 */