Day14.cpp

/*
    Author: Aryan Yadav
    Implement Trie (Prefix Tree)

    Complexity: O(n)
    Algorithm: NA
    Difficulty: Hard
    Data Structure: Trie
*/

class TrieNode
{
public:
    // Initialize your data structure here.
    TrieNode()
    {
        count = 0;
        for (int i = 0; i < 26; ++i)
        {
            next[i] = NULL;
        }
    }

    int count;
    TrieNode *next[26];
};

class Trie
{
public:
    Trie()
    {
        root = new TrieNode();
    }

    ~Trie()
    {
        this->deleteNodes(root);
    }

    // Inserts a word into the trie.
    void insert(string key)
    {
        TrieNode *cur = this->root;
        for (size_t i = 0; i < key.size(); ++i)
        {
            if (cur->next[key[i] - 'a'] == NULL)
            {
                cur->next[key[i] - 'a'] = new TrieNode();
            }
            cur = cur->next[key[i] - 'a'];
        }
        ++cur->count;
    }

    // Returns if the word is in the trie.
    bool search(string key)
    {
        return getTargetCount(key) > 0;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix)
    {
        return this->getTargetCount(prefix) != -1;
    }

    void deleteNodes(TrieNode *node)
    {
        if (node == NULL)
        {
            return;
        }

        for (size_t i = 0; i < 26; ++i)
        {
            this->deleteNodes(node->next[i]);
        }

        delete node;
    }

private:
    int getTargetCount(string key)
    {
        TrieNode *cur = this->root;
        for (size_t i = 0; i < key.size(); ++i)
        {
            if (cur->next[key[i] - 'a'] == NULL)
            {
                return -1;
            }
            cur = cur->next[key[i] - 'a'];
        }
        return cur->count;
    }
    TrieNode *root;
};

/**
 * 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);
 */