208. Implement Trie (Prefix Tree

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

Cautious:

• Don't initialize vector as a member of a class outside any method
• Resize with nullptr rather than reserve
• "=" operator of shared_ptr can be used for reassigning.