208. Implement Trie (Prefix Tree)

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

Problem

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.

• All inputs are guaranteed to be non-empty strings.

Solution

struct Node {
    bool end;
    Node* next[26];
    Node(): next{nullptr}, end(false) {}
};
class Trie {
private:
    Node *const root;
public:
    /** Initialize your data structure here. */
    Trie() : root(new Node()) { 
    }
    
    /** Inserts a word into the trie. */
    void insert(string word) {
        Node *current = root;
        for (const auto c: word) {
            if (!current->next[c - 'a']) current->next[c - 'a'] = new Node();
            current = current->next[c - 'a'];
        }
        current->end = true;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        Node *current = root;
        for (const auto c: word) {
            if (!current->next[c - 'a']) return false;
            current = current->next[c - 'a'];
        }
        return current->end;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        Node *current = root;
        for (const auto c: prefix) {
            if (!current->next[c - 'a']) return false;
            current = current->next[c - 'a'];
        }
        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);
 */

• #prefixtree

• #trie

• #important