trie_tree.cpp

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#include <array>
#include <cassert>
#include <iostream>
#include <memory>
#include <string>

namespace data_structures {
class trie {
 private:
    static constexpr uint8_t NUM_CHARS = 26;  
    std::array<std::shared_ptr<trie>, NUM_CHARS << 1> arr;
    bool isEndofWord = false;  

    uint8_t char_to_int(const char& ch) const {
        if (ch >= 'A' && ch <= 'Z') {
            return ch - 'A';
        } else if (ch >= 'a' && ch <= 'z') {
            return ch - 'a' + NUM_CHARS;
        }
 
        std::cerr << "Invalid character present. Exiting...";
        std::exit(EXIT_FAILURE);
        return 0;
    }

    bool search(const std::shared_ptr<trie>& root, const std::string& str,
                int index) {
        if (index == str.length()) {
            if (!root->isEndofWord) {
                return false;
            }
            return true;
        }
        int j = char_to_int(str[index]);
        if (!root->arr[j]) {
            return false;
        }
        return search(root->arr[j], str, index + 1);
    }
 
 public:
    trie() = default;  

    void insert(const std::string& str) {
        std::shared_ptr<trie> root(nullptr);
 
        for (const char& ch : str) {
            int j = char_to_int(ch);
            if (root) {
                if (root->arr[j]) {
                    root = root->arr[j];
                } else {
                    std::shared_ptr<trie> temp(new trie());
                    root->arr[j] = temp;
                    root = temp;
                }
            } else if (arr[j]) {
                root = arr[j];
            } else {
                std::shared_ptr<trie> temp(new trie());
                arr[j] = temp;
                root = temp;
            }
        }
        root->isEndofWord = true;
    }

    bool search(const std::string& str, int index) {
        if (index == str.length()) {
            if (!isEndofWord) {
                return false;
            }
            return true;
        }
        int j = char_to_int(str[index]);
        if (!arr[j]) {
            return false;
        }
        return search(arr[j], str, index + 1);
    }

    bool deleteString(const std::string& str, int index) {
        if (index == str.length()) {
            if (!isEndofWord) {
                return false;
            }
            isEndofWord = false;
            // following lines - possible source of error?
            // for (int i = 0; i < NUM_CHARS; i++)
            //     if (!arr[i])
            //         return false;
            return true;
        }
        int j = char_to_int(str[index]);
        if (!arr[j]) {
            return false;
        }
        bool var = deleteString(str, index + 1);
        if (var) {
            arr[j].reset();
            if (isEndofWord) {
                return false;
            } else {
                int i = 0;
                for (i = 0; i < NUM_CHARS; i++) {
                    if (arr[i]) {
                        return false;
                    }
                }
                return true;
            }
        }
 
        /* should not return here */
        std::cout << __func__ << ":" << __LINE__
                  << "Should not reach this line\n";
        return false;
    }
};
}  // namespace data_structures

static void test() {
    data_structures::trie root;
    root.insert("Hello");
    root.insert("World");
 
    assert(!root.search("hello", 0));
    std::cout << "hello - " << root.search("hello", 0) << "\n";
 
    assert(root.search("Hello", 0));
    std::cout << "Hello - " << root.search("Hello", 0) << "\n";
 
    assert(!root.search("Word", 0));
    std::cout << "Word - " << root.search("Word", 0) << "\n";
 
    assert(root.search("World", 0));
    std::cout << "World - " << root.search("World", 0) << "\n";
 
    // Following lines of code give erroneous output
    // root.deleteString("hello", 0);
    // assert(!root.search("hello", 0));
    // std::cout << "hello - " << root.search("world", 0) << "\n";
}

int main() {
    test();
 
    return 0;
}