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.
• int countWordsEqualTo(string word): Returns the number of instances of the string word in the trie.
• int countWordsStartingWith(string prefix): Returns the number of strings in the trie that have the string prefix as a prefix.
• void erase(string word): Erases the string word from the trie.

Constraints:

1 <= word.length, prefix.length <= 2000
word and prefix consist only of lowercase English letters.
At most 3 * 10^4 calls in total will be made to insert, countWordsEqualTo, countWordsStartingWith, and erase.
It is guaranteed that for any function call to erase, the string word will exist in the trie.

Example 1:

Input
["Trie", "insert", "insert", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsStartingWith"]
[[], ["apple"], ["apple"], ["apple"], ["app"], ["apple"], ["apple"], ["app"], ["apple"], ["app"]]
Output
[null, null, null, 2, 2, null, 1, 1, null, 0]

Explanation
Trie trie = new Trie();
trie.insert("apple"); // Inserts "apple".
trie.insert("apple"); // Inserts another "apple".
trie.countWordsEqualTo("apple"); // There are two instances of "apple" so return 2.
trie.countWordsStartingWith("app"); // "app" is a prefix of "apple" so return 2.
trie.erase("apple"); // Erases one "apple".
trie.countWordsEqualTo("apple"); // Now there is only one instance of "apple" so return 1.
trie.countWordsStartingWith("app"); // return 1
trie.erase("apple"); // Erases "apple". Now the trie is empty.
trie.countWordsStartingWith("app"); // return 0

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**Submission link:**https://www.codingninjas.com/codestudio/problems/implement-trie_1387095

class TrieNode
{
    TrieNode* links[26];
    public:
    int word_count=0;
    int prefix_count=0;
    
    bool containsKey(char ch)
    {
        return links[ch-'a']!=NULL;
    }
    
    void putNode(char ch,TrieNode* node)
    {
        links[ch-'a']=node;
    }
    
    TrieNode* getNode(char ch)
    {
        return links[ch-'a'];
    }
};

class Trie {
    TrieNode* root;
public:
    Trie() 
    {
        root=new TrieNode();
    }
    
    void insert(string word) 
    {
        TrieNode* node=root;
        for(auto &ch:word)
        {
            if(!node->containsKey(ch))
                node->putNode(ch,new TrieNode());
            
            node->prefix_count++;
            node=node->getNode(ch);
        }
        
        node->prefix_count++;
        node->word_count++;
    }
    
    int countWordsEqualTo(string word) 
    {
        TrieNode* node=root;
        for(auto &ch:word)
        {
            if(!node->containsKey(ch))
                return 0;
            
            node=node->getNode(ch);
        }
        
        return node->word_count;
    }
    
    int countWordsStartingWith(string prefix) 
    {
         TrieNode* node=root;
        for(auto &ch:word)
        {
            if(!node->containsKey(ch))
                return 0;
            
            node=node->getNode(ch);
        }
        
        return node->prefix_count;
    }
    
    void erase(string word)
    {
        TrieNode* node=root;
        for(auto &ch:word)
        {
            if(node->prefix_count>0)
            node->prefix_count--;
            else
                return;
            node=node->getNode(ch);
        }
        
        node->prefix_count--;
        if(node->word_count>0)
            node->word_count--;
    }
};