Morse tree - please access https://paulosuzart.github.io/blog/2020/04/30/morse-and-trees/

MorseTreeChallenge.java

package com;

import static java.lang.String.valueOf;
import static java.util.Objects.isNull;
import static java.util.Objects.nonNull;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.stream.Collectors;

public class MorseTreeChallenge {

  private static char[] ENGLISH = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
    'y', 'z', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0',
    ',', '.', '?'};

  private static String[] MORSE = {".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..",
    ".---", "-.-", ".-..", "--", "-.", "---", ".---.", "--.-", ".-.",
    "...", "-", "..-", "...-", ".--", "-..-", "-.--", "--..", ".----",
    "..---", "...--", "....-", ".....", "-....", "--...", "---..", "----.",
    "-----", "--..--", ".-.-.-", "..--.."};

  private static final MorseTree morseTree = new MorseTree(ENGLISH, MORSE);

  private static class Signal {

    String morse = "";
    String symbol;
    Signal dash; // reference to next signal whose prefix corresponds to current signal
    Signal dot; // reference to next signal whose prefix corresponds to current signal

    @Override
    public String toString() {
      return "Signal{" +
        "morse='" + morse + '\'' +
        ", alpha='" + symbol + '\'' +
        '}';
    }

  }

  private static class MorseTree {

    Signal root = new Signal();

    /**
     * Takes a sized arrays with english chars and corresponding morse codes for them.
     *
     * @param ENGLISH array of chars
     * @param MORSE array of respective morse codes
     */
    MorseTree(char[] ENGLISH, String[] MORSE) {
      for (int i = 0; i < MORSE.length; i++) {
        insert(MORSE[i], ENGLISH[i]);
      }
    }

    private void addToSearch(LinkedList<Signal> signals, Signal node) {
      if (isNull(node)) {
        return;
      }
      signals.addFirst(node);
    }

    List<Signal> fuzzyMatch(String signal) {
      var result = new ArrayList<Signal>();
      var toSearch = new LinkedList<Signal>();

      toSearch.add(root);

      while (!toSearch.isEmpty()) {
        Signal curr = toSearch.remove(0);

        if (curr.morse.length() == signal.length() && nonNull(curr.symbol)) {
          result.add(curr);
          continue;
        }

        switch (signal.charAt(curr.morse.length())) {
          case '.':
            addToSearch(toSearch, curr.dot);
            break;
          case '-':
            addToSearch(toSearch, curr.dash);
            break;
          default:
            addToSearch(toSearch, curr.dash);
            addToSearch(toSearch, curr.dot);
        }
      }
      return result;
    }

    private Signal insert(String signal, char alpha) {
      Signal currentNode = root;
      for (int i = 0; i < signal.length(); i++) {
        var step = signal.charAt(i);

        if (step == '.') {
          if (isNull(currentNode.dot)) {
            currentNode.dot = new Signal();
            currentNode.dot.morse = signal.substring(0, i + 1);
          }
          currentNode = currentNode.dot;
        } else {
          if (isNull(currentNode.dash)) {
            currentNode.dash = new Signal();
            currentNode.dash.morse = signal.substring(0, i + 1);
          }
          currentNode = currentNode.dash;
        }
      }
      currentNode.symbol = valueOf(alpha).toUpperCase();
      currentNode.morse = signal;
      return currentNode;
    }
  }

  public static List<String> possibilities(String signals) {
    return morseTree.fuzzyMatch(signals).stream().map(s -> s.symbol).collect(Collectors.toList());

  }

  public static void main(String[] args) {
    System.out.println(".      Expect E = " + possibilities("."));
    System.out.println("-      Expect T = " + possibilities("-"));
    System.out.println("?      Expect E or T = " + possibilities("?"));
    System.out.println("..-    Expect U = " + possibilities("..-"));
    System.out.println(".??    Expect S, U, R, W = " + possibilities(".??"));
    System.out.println(".--    Expect W = " + possibilities(".--"));
    System.out.println("?.     Expect I or N = " + possibilities("?."));
    System.out.println(".?     Expect I or A = " + possibilities(".?"));
    System.out.println("..--.. Expect ? = " + possibilities("..--.."));
    System.out.println("..-.   Expect F = " + possibilities("..-."));
    System.out.println("..---  Expect 2 = " + possibilities("..---"));
    System.out.println("---..  Expect 8 = " + possibilities("---.."));
    System.out.println("----.  Expect 9 = " + possibilities("----."));
    System.out.println("-----  Expect 0 = " + possibilities("-----"));
    System.out.println("----?  Expect 9 or 0 = " + possibilities("----?"));
  }

}