What am I doing wrong? I feel like the instructions could be more clear.

Question about the task

Inverted words

Java Multithreading, Level 2, Lesson 9

Under discussion

When I print out result for testing I get: rat tar a a tot tot

In the main method, read the name of a file that contains words separated by spaces from the console.
In the text of the file, find all pairs of words that are mirror images of each other. Add them to result.
Use StringBuilder.
The file encoding is UTF-8.

Example of file contents

rat tar tart a
a tot tot tot

Output:

rat tar
a a
tot tot

Requirements:

The main method must read the filename from the keyboard.
The main method must use StringBuilder.
The Solution class must contain a nested Pair class with equals, hashCode, and toString methods. Don't delete or change these methods.
The Pair class must declare a constructor without parameters, i.e. a default constructor.
The result list must be filled with correct pairs according to the task conditions.

package com.codegym.task.task22.task2207; import java.io.BufferedReader; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.util.*; /* Inverted words */ public class Solution { public static List<Pair> result = new LinkedList<>(); public static void main(String[] args) throws IOException { // read filename from console Scanner scanner = new Scanner(System.in); String fileName = scanner.nextLine(); // String fileName = "C:\\Users\\Andrew Cate\\CodeGym\\CodeGymTasks\\3.JavaMultithreading\\src\\com\\codegym\\task\\task22\\task2207\\test.txt"; // read the file contents into a list BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName))); List<String> fileContents = new ArrayList<>(); while (bufferedReader.ready()) { String line = bufferedReader.readLine(); String[] array = line.split(" "); fileContents.addAll(Arrays.asList(array)); } // process the list, adding valid pairs to result list for (int i = 0; i < fileContents.size() - 1; i++) { // create a pair with the next two items in list Pair pair = new Pair(); pair.first = fileContents.get(i); pair.second = fileContents.get(i + 1); // create another pair with first being current item from list and second being reverse of first Pair reversePair = new Pair(); StringBuilder stringBuilder = new StringBuilder(fileContents.get(i)); reversePair.first = stringBuilder.toString(); reversePair.second = stringBuilder.reverse().toString(); // compare pairs and add to list if equal and not already in the list if (pair.equals(reversePair)) if (!result.contains(pair)) result.add(pair); } // print pairs for testing // for (Pair p : // result) { // System.out.println(p.first + " " + p.second); // } scanner.close(); bufferedReader.close(); } public static class Pair { String first; String second; @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Pair pair = (Pair) o; if (first != null ? !first.equals(pair.first) : pair.first != null) return false; return second != null ? second.equals(pair.second) : pair.second == null; } @Override public int hashCode() { int result = first != null ? first.hashCode() : 0; result = 31 * result + (second != null ? second.hashCode() : 0); return result; } @Override public String toString() { return first == null && second == null ? "" : first == null ? second : second == null ? first : first.compareTo(second) < 0 ? first + " " + second : second + " " + first; } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

8 April 2019, 18:12

It looks like your output falls apart when i change the file to be: rat tar tart a a tot tot tot tot tart rat I haven't specifically determined where the problem is, however I can share how I solved my task:

// cache to hold values for testing
HashSet<String> values = new HashSet

while(br.ready()){
   //read the line
   String line = br.readline();
   for(String x: line.split(" "))
   {
      //check if the reverse value is already contained
      //if it is then remove it, add the 2 words to result
      if(values.contains(x.reverse()){
         values.remove(x.reverse());
         result.add(new pair(x, x.reverse());
      //otherwise add the word to the hashset
      }else
          values.add(x)
   }
}

This code won't compile, as strings don't support .reverse() and the Pair class doesn't have a constructor that takes two strings, and i don't think it will verify without the default constructor. You should be able to intuit how to either modify your existing code or redo the task to solve with this.

+13

Guadalupe Gagnon

Level 37 , Tampa, United States

8 April 2019, 18:17

line 47 of your code states: "only adds if it is not contained in the list" This is probably your issue as there may be more than 1 pair that are reverse of each other. In the change I made above to add words, this made tot repeat 4 times (being 2 full pairs), but your code only output 'tot tot' once

Andrew

Level 29 , Seattle, United States

8 April 2019, 21:23

Great tips! Thanks, I got it to pass. You were right if it had 2 pairs of a word and reverse, it would only get one. Great idea adding unpaired words to a Set and removing them when paired. I also had some unnecessary additional Pairs for comparing. Maybe I just wanted to use the methods they overrided. That toString() was crazy!

Bill Wu

Level 29 , Wellington, New Zealand

8 April 2019, 21:41

I used Guadalupe's logic to pass the verification, but my original code could get same result with the testing data rat tar tart a a tot tot tot tot tart rat However it failed. Weird. I used the pair in a while loop to check each pair has the mirrored first and second. If so it will be added to the result, and move on to the next pair. else the second will be the first of next pair.

Surya

Level 33 , Newark, United States

14 June 2020, 06:02

Guadalupe, good solution. It turned on light in my brain. Thank you.