Can't satisfy last condition. I have the right output.

Question about the task

Inverted words

Java Multithreading, Level 2, Lesson 9

Under discussion

I have no idea what to do anymore

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.FileReader; 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 { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); FileReader fileReader = new FileReader(reader.readLine()); Scanner scanner = new Scanner(fileReader); while (scanner.hasNext()){ String line = scanner.nextLine(); String[] arr = line.split(" "); ArrayList<String> list = new ArrayList<>(Arrays.asList(arr)); for (String y : arr){ StringBuilder stringBuilder = new StringBuilder(y); if (list.contains(stringBuilder.reverse().toString())){ list.remove(stringBuilder.toString()); Pair pair = new Pair(); pair.first = y; pair.second = stringBuilder.toString(); result.add(pair); } } } for (int i = 0 ; i <result.size()-1;i++){ for (int j = i+1 ; j < result.size(); j++){ if (result.get(i).first.equals(result.get(j).second)){ result.remove(result.get(j)); } } } for (int i = 0 ; i < result.size(); i++){ System.out.println(result.get(i).first + " "+ result.get(i).second); } } public static class Pair { String first; String second; Pair(){} @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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Samuel Schmid

Level 4 , Rothrist, Switzerland

7 August 2020, 17:19

When I test your program I see 2 issues: 1. You list words that have no mirror word in the result as well 2. You list some words multiple times if they occur more than twice in the text Example input:

c h
tot tot tot
a b
tar rat

Expected output:

tot tot
tar rat

But your solution returns

c c
h h
tot tot
tot tot
a a
b b
tar rat

David

Level 26 , Bucharest, Romania

11 August 2020, 08:10

I got it, I understand, but I have fixed that issue in the second alternative below, still can't pass last condition

David

Level 26 , Bucharest, Romania

7 August 2020, 16:12

Here I have another way of solving...still doesn't pass even though I have the right output

public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        FileReader fileReader = new FileReader(reader.readLine());
        ArrayList<String> list = new ArrayList<>();
        Scanner scanner = new Scanner(fileReader);
        while (scanner.hasNext()){
            String line = scanner.nextLine();
            String[] arr = line.split(" ");
            for (int i = 0 ; i < arr.length; i++){
                list.add(arr[i]);
            }
        }
        for (int i = 0 ; i < list.size();i++){
            StringBuilder stringBuilder = new StringBuilder(list.get(i));
            StringBuilder s = stringBuilder.reverse();
            if (list.contains(s.toString())){
                Pair pair  = new Pair();
                pair.first =list.get(i);
                pair.second = s.toString();
                result.add(pair);
                for (int j = 0; j < list.size(); j++){
                    if (list.get(j).equals(stringBuilder.toString()) || list.get(j).equals(stringBuilder.reverse().toString())){
                        list.remove(list.get(j));
                    }
                }

            }

        }
}

Samuel Schmid

Level 4 , Rothrist, Switzerland

9 September 2020, 03:45

Sorry haven't been on here for a while. I'll give you another hint: Your for loop in lines 21-25 has a problem. You are looping over a list and then removing items from it while you do so. This can be dangerous, as you are changing the list but you are not updating the index you use for accessing it. Let's have a quick example to see what can go wrong:

ArrayList<Integer> list = new ArrayList<>();
list.add(2);
list.add(3);
list.add(5);
list.add(6);
for (int i = 0; i < list.size(); i++) {
    if (list.get(i) % 2 == 1) {
        // The element is odd -> remove it.
        list.remove(list.get(i));
    }
}

Here we have a simple program, we have a list of 4 numbers, and we want to remove all odd numbers. We start out with [2, 3, 5, 6]. Loop starts i = 0 list.get(i) = 2 2 is not odd Loop continues i = 1 list.get(i) = 3 3 is odd -> 3 gets removed -> list is now [2, 5, 6] Loop continues i = 2 (this is the problem) list.get(i) = 6 6 is not odd Loop ends (because 3 < list.size() is false) We just skipped over the number 5 in the list. When you remove an item from a list, all the items to the right of it get shifted down one, so their index is reduced. If you are holding an index on that list, you also need to shift that index in order to not skip any elements. There are a couple possible solutions to this problem: 1. After list.remove(...) you cn call j-- to adjust for that. (I'm not sure if there will be problems with the index i from the outer loop, but I don't think so) 2. Use Iterator<String> to traverse the loop, Iterator has a method .remove which covers the problem with the shifting elements and works like it should 3. Keep the way you are iterating over the list, but instead of going from 0 - (size() - 1) go from top to bottom, so something like for(int j = list.size()-1; i >= 0; i--) { ... That way, you have already processed the shifting elements and