Trie Data Structure using smart pointer and OOP in C++

We will implement trie using smart pointers in C++ and OOP. Here, We have already discussed the implementation of trie data using recursion
In our implementation node of a trie look like : 

CPP

class TrieNode{

    public:
    // Use of shared_ptr for storing Children
    // Pointers of TrieNode

    shared_ptr children[ALPHABET_SIZE];

    // Tracks whether If this Node is the end of
    // any word stored in Trie

    bool isWord;

    // Constructor for TrieNode
    TrieNode()
    {
        for(int i=0; i<ALPHABET_SIZE; i++)
        {
            children[i] = shared_ptr();
        }
        isWord = false;
    }
};

The interface is the class showing the functionalities of our object class which has only pure virtual functions. Here, the concept interface discussed in more detail.

CPP

// Interface representing functionalities
// of Trie Data Structure
class interface {
public:
    interface() {}
    virtual ~interface() {}
    // Pure virtual functions showing all
    // the functions of my Trie class

    // To convert character to integer like hashing
    virtual int i2c(char) = 0;

    // Inserts word to Trie
    virtual void insertWord(string&) = 0;

    // Deletes word if present
    virtual bool deleteWord(string&) = 0;

    // To search a word in Trie
    virtual bool searchWord(string&) = 0;

    // Checks whether there is any children present
    // for any node
    virtual bool isEmptyNode(shared_ptr<TrieNode>)
                                          const = 0;
};

nullptrs stores NULL which suggests that there is no path for any other string from that position
Below image shows the insertion of “geeks” into an empty trie. 

Below image shows the insertion of “geeksfor” into the trie. geeks p is already exiting in the trie. so, it overlaps.

Below image shows the insertion of “trie” into the trie

Why shared_ptr instead of all other smart pointers (auto_ptr, unique_ptr, weak_ptr)?
We are using shared_ptr due to the fact that while constructing the Trie we may encounter a situation where we may have to share the resource of a particular pointer to the other temporary shared_ptr to traverse Trie. In that shared_ptr is better than any other above mentioned pointers.
Below is the implementation of the above approach :

CPP

#include <iostream>

// For shared_ptr class
#include <memory>

using namespace std;
#define ALPHABET_SIZE 26

// Trie Node class
class TrieNode {

public:
    // Use of shared_ptr for storing Children
    // Pointers of TrieNode

    shared_ptr<TrieNode> children[ALPHABET_SIZE];

    // Tracks whether If this Node is the end of
    // any word stored in Trie

    bool isWord;

    // Constructor for TrieNode
    TrieNode()
    {
        for (int i = 0; i < ALPHABET_SIZE; i++) {
            children[i] = shared_ptr<TrieNode>();
        }
        isWord = false;
    }
};

// Interface representing functionalities
// of Trie Data Structure
class interface {
public:
    interface() {}
    virtual ~interface() {}
    // Pure virtual functions showing all
    // the functions of my Trie class

    // To convert character to integer like hashing
    virtual int i2c(char) = 0;

    // Inserts word to Trie
    virtual void insertWord(string&) = 0;

    // Deletes word if present
    virtual bool deleteWord(string&) = 0;

    // To search a word in Trie
    virtual bool searchWord(string&) = 0;

    // Checks whether there is any children present
    // for any node
    virtual bool isEmptyNode(shared_ptr<TrieNode>)
                                          const = 0;
};

class Trie : public interface {

    // Storing root of the Trie
    shared_ptr<TrieNode> root;
    int Total_words;

public:
    Trie()
    {
        root = shared_ptr<TrieNode>
                              (new TrieNode());
        Total_words = 0;
    }

    ~Trie()
    {
        // Need not delete anything
                // as shared_ptr deallocates
                // all memory automatically
    }

    // To convert characters of string into
    // integer like hashing of character
    int i2c(char c)
    {
        return static_cast<int>(c - 'a');
    }

    // Insert word function
    void insertWord(string& trieString)
    {
        shared_ptr<TrieNode> current = root;
        for (int i = 0; i < trieString.size(); i++)
                {

            // If word after some prefix is not
                        // present then creates new node
            if (current->children[i2c(trieString[i])] ==
                          shared_ptr<TrieNode>(nullptr))
            {
                current->children[i2c(trieString[i])] =
                     shared_ptr<TrieNode>(new TrieNode());
            }
            current = (current->children[i2c(trieString[i])]);
        }

        // Now word is added in Trie so at leaf node
        // for that word isWord=true
        current->isWord = true;
    }

    // Searching for word whether it is
    // present in Trie
    bool searchWord(string& trieString)
    {
        shared_ptr<TrieNode> current = root;

        for (int i = 0; i < trieString.size(); i++)
        {
            // If at any point in Trie Node for particular
            // character is not present means nullptr then
            // return false
            if (current->children[i2c(trieString[i])] ==
                            shared_ptr<TrieNode>(nullptr))
                return false;
            current = current->children[i2c(trieString[i])];
        }

        // At the end of the word checking whether this
        // word is really present or not
        if (current->isWord == true)
            return true;

        return false;
    }

    bool Partdelete(string& trieString, shared_ptr<TrieNode>&
                                                     checkout)
    {
        // Word is not present in the Trie then returns
        // false and stops further recursion
        if (checkout == nullptr)
            return false;

        // At the end of the word if the word is
        // present in trie then setting isWord to
        // false either returning false
        if (trieString.size() == 0) {
            if (checkout->isWord == true) {
                checkout->isWord = false;
                return true;
            }
            return false;
        }

        // String excluding first character
        string part = trieString.substr(1);

        // Recursive call to Partdelete for
        // rest of the string(part)
        if (Partdelete(part, checkout->
                      children[i2c(trieString[0])])) {

            // Checks whether it is empty node
            // then delete this node
            if (isEmptyNode(checkout->
                      children[i2c(trieString[0])])) {

                // Resetting memory and making it nullptr
                checkout->children[i2c(trieString[0])].
                                                 reset();

                checkout->children[i2c(trieString[0])] =
                                                  nullptr;

                return true;
            }
            else
                return true;
        }
        else
            return false;

        return false;
    }

    // For ease of recursion; passing
    // root to Partdelete
    bool deleteWord(string& trieString)
    {
        if (Partdelete(trieString, root))
            return true;
        return false;
    }

    // Checks whether there is no children present
    bool isEmptyNode(shared_ptr<TrieNode> check) const
    {
        for (int i = 0; i < ALPHABET_SIZE; i++) {
            if (check->children[i] != nullptr ||
                              check->isWord == true)
                return false;
        }
        return true;
    }
};

// Driver code
int main()
{
    // Again using shared_ptr to store Trie
    // you can use auto_ptr here
    shared_ptr<Trie> myTrie(new Trie());

    string word1 = "geeksfor";
    string word2 = "geeksforgeeks";
    string word3 = "nothing";

    myTrie->insertWord(word1);

    if (myTrie->searchWord(word1))
        cout << word1 << ": Is Present" << endl;
    else
        cout << word1 << ": Not Present" << endl;

    if (myTrie->searchWord(word3))
        cout << word3 << ": Is Present" << endl;
    else
        cout << word3 << ": Not Present" << endl;

    myTrie->insertWord(word2);

    if (myTrie->deleteWord(word2))
        cout << word2 << ": Successfully deleted" << endl;
    else
        cout << word2 << ": Not Present" << endl;

    if (myTrie->searchWord(word2))
        cout << word2 << ": Is Present" << endl;
    else
        cout << word2 << ": Not Present" << endl;

}

Output:

geeksfor: Is Present
nothing: Not Present
geeksforgeeks: Successfully deleted
geeksforgeeks: Not Present

Time Complexity:  O(n*s) where n is the number of words and s is the maximum length of the word in the list of words.
Auxiliary Space:  O(n*ALPHABET_SIZE)