Java Program to Implement Hash Trie

Last Updated : 02 Feb, 2021

A trie isn't something CS students might have spent that much time on in college but it's really very important for interviews. A trie is a data structure that is actually a type of tree, but it's often used to store an associative array or a dynamic set where the keys are usually characters or strings, and its position in the tree defines the key with which it is associated. The way that it works is that every successor of a node have a common prefix of the string associated with that node which means each node might store a, just a character as its data but then if we look at the path from the root down to that node, that note is really representing a word or a part of a word, and so what allows us to do is, very quick lookups of a particular kind of word or character.

Java Code:

Importing required module:

Java

import java.io.*;
import java.util.*;

Now, we will make a class TrieHash in which we will implement a HashMap, it will also contain two constructors with zero and single array argument, a function to add characters to hash trie and a function to search for the specific string in the hash trie.

Java

class TrieHash {

    // implementing a HashMap
    private HashMap<Character, HashMap> origin;

    // implementing a zero-argument constructor
    public TrieHash()
    {
        // creating a new HashMap
        origin = new HashMap<Character, HashMap>();
    }

    // implementing another constructor
    // with an array as a parameter
    public TrieHash(String[] array)
    {
        origin = new HashMap<Character, HashMap>();
        // attaching that array string in the trie
        for (String c : array)
            attach(c);
    }

    // attach function to add character to the trie
    public void attach(String str)
    {
        HashMap<Character, HashMap> node = origin;
        int i = 0;
        while (i < str.length()) {
            // if node already contains that key,
            //  we will simply point that node
            if (node.containsKey(str.charAt(i))) {
                node = node.get(str.charAt(i));
            }
            else {

                // else we will make a new hashmap with
                // that character and then point it.
                node.put(str.charAt(i),
                         new HashMap<Character, HashMap>());
                node = node.get(str.charAt(i));
            }
            i++;
        }

        // putting 0 to end the string
        node.put('\0', new HashMap<Character, HashMap>(0));
    }

    // function to search for the specific
    // string in the hash trie
    public boolean search(String str)
    {
        HashMap<Character, HashMap> presentNode = origin;
        int i = 0;
        while (i < str.length()) {

            // will search for that character if it exists
            if (presentNode.containsKey(str.charAt(i))) {
                presentNode
                    = presentNode.get(str.charAt(i));
            }
            else {
                // if the character does not exist
                // that simply means the whole string
                // will also not exists, so we will
                // return false if we find a character
                // which is not found in the hash trie
                return false;
            }
            i++;
        }
        // this will check for the end string,
        // and if the whole string is found,
        // it will return true else false
        if (presentNode.containsKey('\0')) {
            return true;
        }
        else {
            return false;
        }
    }
}

Now all the required functions are coded, now we will test those functions with the user input. For this, we will again make a new class to test our hash trie which will prompt the user to enter the words for trie and the word to be searched for.

Java

public class Main {
    // unreported exception IOException must be caught or
    // declared to be thrown
    public static void main(String[] args)
        throws IOException
    {
        BufferedReader br
            = new BufferedReader(new InputStreamReader(
                System.in)); // this will accepts the words
                             // for the hash trie
        System.out.println(
            "Enter the words separated with space to be entered into trie");

        // will read the line which user will
        // provide with space separated words
        String input = br.readLine();

        // it will split all the words
        // and store them in the string array
        String[] c = input.split(" ");

        // now we will use constructor with string array as
        // parameter and we will pass the user entered
        // string in that constructor to construct the hash
        // trie
        TrieHash trie = new TrieHash(c);
        System.out.println(
            "\nEnter the word one by one to be searched in hash-trie");
        String word = br.readLine();

        // this will search for the word in out trie
        if (trie.search(word)) {
            System.out.println("Word Found in the trie");
        }
        else {
            System.out.println(
                "Word NOT Found in the trie!");
        }
    }
}

Below is the implementation of the problem statement:

Java

import java.io.*;
import java.util.*;

class TrieHash {

    // implementing a HashMap
    private HashMap<Character, HashMap> origin;

    // implementing a zero-argument constructor
    public TrieHash()
    {

        // creating a new HashMap
        origin = new HashMap<Character, HashMap>();
    }

    // implementing another constructor
    // with an array as a parameter
    public TrieHash(String[] array)
    {
        origin = new HashMap<Character, HashMap>();
        // attaching that array string in the trie
        for (String c : array)
            attach(c);
    }

    // attach function to add
    // character to the trie
    public void attach(String str)
    {
        HashMap<Character, HashMap> node = origin;
        int i = 0;
        while (i < str.length()) {
            // if node already contains thatkey,
            // we will simply point that node
            if (node.containsKey(str.charAt(i))) {
                node = node.get(str.charAt(i));
            }
            else {
                // else we will make a new hashmap with
                // that character and then point it.
                node.put(str.charAt(i),
                         new HashMap<Character, HashMap>());
                node = node.get(str.charAt(i));
            }
            i++;
        }

        // putting 0 to end the string
        node.put('\0', new HashMap<Character, HashMap>(0));
    }

    // function to search for the
    // specific string in the hash trie
    public boolean search(String str)
    {
        HashMap<Character, HashMap> presentNode = origin;
        int i = 0;
        while (i < str.length()) {
            // will search for that character
            // if it exists
            if (presentNode.containsKey(str.charAt(i))) {
                presentNode
                    = presentNode.get(str.charAt(i));
            }
            else {
                // if the character does notexist that
                // simply means the whole string will
                // also not exists, so we will return
                // false if we find a character which
                // is not found in the hash trie
                return false;
            }
            i++;
        }
        // this will check for the end string,
        // and if the whole string is found,
        // it will return true else false
        if (presentNode.containsKey('\0')) {
            return true;
        }
        else {
            return false;
        }
    }
}

public class Main {
    // unreported exception IOException
    // must be caught or declared to be thrown
    public static void main(String[] args)
        throws IOException
    {

        // this will accepts the words for the hash trie
        BufferedReader br = new BufferedReader(
            new InputStreamReader(System.in));
        System.out.println(
            "Enter the words separated with space to be entered into trie");
        // will read the line which user will
        // provide with space separated words
        String input = br.readLine();

        // it will split all the words and
        // store them in the string array
        String[] c = input.split(" ");

        // now we will use constructor with string
        // array as parameter and we will pass the
        // user entered string in that constructor
        // to construct the hash trie
        TrieHash trie = new TrieHash(c);
        System.out.println(
            "How many words you have to search in the trie");
        String count = br.readLine();
        int counts = Integer.parseInt(count);
        for (int i = 0; i < counts; i++) {
            System.out.println(
                "\nEnter the word one by one to be searched in hash-trie ");
            String word = br.readLine();
            // this will search for the word in out trie
            if (trie.search(word)) {
                System.out.println(
                    "Word Found in the trie");
            }
            else {
                System.out.println(
                    "Word NOT Found in the trie!");
            }
        }
    }
}