In lecture, we talked about how we can use recursion exploration to print out all permutations of a given string.


WordSplit Printer Material from Lecture  09 will be helpful here. In lecture, we talked about how we can use  recursion exploration to print out all permutations of a given string.  For example, we could use recursion on the input “goat” to print out:  tgoa tgao toga goat gota gaot gato gtoa gtao ogat ogta oagt oatg otga  otag agot agto aogt aotg atgo atog toag tago taog Most of these aren’t  actual anagrams, because they’re gibberish. We could check which are  actual words (like “toga”), but that wouldn’t be enough. There are also  cases like “atgo” where the full string isn’t a word, but we can break  it into the separate words “at” and “go”. To find all anagrams, then, we  need to find the ways we can take one of these permutations and split  it into separate English words. That’s where your method,  findWordsplits, comes in: public void findWordSplits(String input,  TreeSet<String> allWords) { // TODO: Implement this. }   The method takes two parameters: input and allWords. input will be a  string like “atgo” or “goat” that you’re trying to split into separate  words. You do not need to find permutations of input, since that was  part of the demo we did in class. input will be a string whose character  ordering is already set. allWords is a set containing the words listed  in the “words.txt” file — nearly 10,000 English words. allWords is  already populated for you! You’ll need to use it when you’re splitting  up the input string, since each chunk needs to be an actual word. . Your  task is to implement findWordsSplits to find every way you can split  input into valid English words, where every character in input is used  exactly once. For example, if input is we would expect these two splits  to be printed: “goat”, go at goat Other arrangements, such as “g oat” or  “goat”, would not be printed because “g”, “goa”, and “t” are not  considered words. The main method uses “isawabus” as input. Once  findWordsSplits is correctly implemented, you should see the following  output: i saw a bus i saw ab us is aw a bus is aw ab us If the exact  ordering is not the same, that’s completely fine. I’ve provided an  already implemented method in the starter code called printWordsplit:  public void printWordSplit(ArrayList<String> words) { // Already  implemented for you. } You should call printWordSplit to print out a  single arrangement. For the “i saw a bus” example above, you would call  printWordSplit passing in an ArrayList<String> containing [“i”,  “saw”, “a”, “bus” ] to print it out. findWordSplits is a recursion  exploration problem, just like our permutations demo in lecture. Think  about how to apply the recursion exploration formula:   1. How do you represent a path of options you’re exploring? o  printWordsplit is a major hint — if you need an ArrayList<String>  to print a word split, that would also be a convenient way to represent  a path. 2. At each step, what are your options? o Consider an example  like “isawabus”. We can actually list out every possible option for the  next word: i is isa isaw isawa isawab isawabu isawabus Not all of these  are words, so you’ll need to check for yourself which ones are valid  options using the allWords set. The TreeSet<String> is just a  specific type of Set, so you can use any Set methods on it. 3. What do  you do when you’ve finished exploring a path? o Just call  printWordsplit! Another hint: in your implementation, you will need to  use the String’s substring method to split a string into two parts. • To  get a substring that contains the first i characters, use  str.substring(0, i) where str is the name of your String variable. To  get the rest of that string (i.e. everything other than the first i  characters), use str.substring(i). If you’re struggling to translate the  above into actual code, I strongly recommend revisiting Lecture 09 and  see how we applied the same formula to the permutations problem or the  password guessing problem. WordSplitChecker Material from Lecture 10  will be helpful here. If you were able to complete WordSplitPrinter,  then congratulations! You’ve already done most of the hard work for this  last step. In WordSplitChecker

package edu.csc220.recursion;

import java.util.*;

public class WordSplitPrinter {
     * Finds and prints out every possible way to split the input String into individual, valid English words (including
     * if input is itself a single valid word). You must call printWordSplit below to actually print out the results.
    public void findWordSplits(String input, TreeSet<String> allWords) {
        // TODO: Implement this.

    /** Prints out a word split, i.e. one particular arrangement of words. This is implemented for you! */
    private void printWordSplit(ArrayList<String> words) {
        if (words.isEmpty()) {
            System.out.println("(empty word list)");
        } else {
            for (int i = 1; i < words.size(); i++) {
                System.out.print(" " + words.get(i));

    public static void main(String[] args) {
        TreeSet<String> dictionary = readWords();
        WordSplitPrinter wordSplitPrinter = new WordSplitPrinter();

        // Expected to print out:
        // i saw a bus
        // i saw ab us
        // is aw a bus
        // is aw ab us
        wordSplitPrinter.findWordSplits("isawabus", dictionary);

    // Reads the "words.txt" file and returns the words in a TreeSet<String>. This is completely implemented for you!
    private static TreeSet<String> readWords() {
        TreeSet<String> allWords = new TreeSet<>();
        try {
            BufferedReader bufferedReader = new BufferedReader(new FileReader("words.txt"));
            String line;
            while ((line = bufferedReader.readLine()) != null) {
                if (line.trim().isEmpty()) {
        } catch (IOException exception) {
            throw new RuntimeException(exception);
        return allWords;

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