The result list must be filled with correct pairs according to the task conditions.

Question about the task

Inverted words

Java Multithreading, Level 2, Lesson 9

Under discussion

It prints the correct output but it fails at the last requirement. A little help please ? :D Thank you!

package com.codegym.task.task22.task2207;

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

/*
Inverted words

*/
public class Solution {
    public static List<Pair> result = new LinkedList<>();


    public static void main(String[] args) throws IOException {
        ArrayList<String> wordsList = new ArrayList<String>();
        Map<String, String> map = new LinkedHashMap<>();

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String filename = reader.readLine();

        File file = new File(filename);
        Scanner scan = new Scanner(file);

        while((scan.hasNext()))
        {
            wordsList.add(scan.next());
        }


        for(int i = 0; i < wordsList.size() - 1; i++)
        {
            for(int j = i + 1; j < wordsList.size(); j++)
            {

                StringBuilder sb = new StringBuilder(wordsList.get(j));
                if(wordsList.get(i).equals(sb.reverse().toString()))
                {
                    map.put(wordsList.get(i), sb.reverse().toString());
                }
            }
        }
        Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
        while(iterator.hasNext())
        {
            Map.Entry<String, String> pairMap = iterator.next();
            Pair pair = new Pair();
            pair.first = pairMap.getKey();
            pair.second = pairMap.getValue();
            result.add(pair);

        }

    }

    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;
        }
    }

}

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.*; import java.util.*; /* Inverted words */ public class Solution { public static List<Pair> result = new LinkedList<>(); public static void main(String[] args) throws IOException { ArrayList<String> wordsList = new ArrayList<String>(); Map<String, String> map = new LinkedHashMap<>(); BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String filename = reader.readLine(); File file = new File(filename); Scanner scan = new Scanner(file); while((scan.hasNext())) { wordsList.add(scan.next()); } for(int i = 0; i < wordsList.size() - 1; i++) { for(int j = i + 1; j < wordsList.size(); j++) { StringBuilder sb = new StringBuilder(wordsList.get(j)); if(wordsList.get(i).equals(sb.reverse().toString())) { map.put(wordsList.get(i), sb.reverse().toString()); } } } Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator(); while(iterator.hasNext()) { Map.Entry<String, String> pairMap = iterator.next(); Pair pair = new Pair(); pair.first = pairMap.getKey(); pair.second = pairMap.getValue(); result.add(pair); } } 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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Seb

Level 41 , Crefeld, Germany

16 January 2020, 10:34

I can see that your program gives the expected result for the given example input. Nevertheless, there are a few problems here. Change the example file input for instance to the following content: rat tar tart a a tot tot tot rat tot a tot Your program will now give the following output: rat tar rat tar a a tot tot The output should be as follows though: rat tar a a tot tot tot tot That means that your program creates two pairs for rat and tar although there really is only one pair - and at the same time your program creates only one pair for tot and tot although there should be two pairs. A few hints: If you find two matching elements in the list, you might consider deleting them, so that those elements won't give you extra matches. It's not easy to iterate through a list and change the list's content at two places at the same time. Maybe a copy of the wordlist can help? Maybe you can work with an extra set to store unmatched variables while looping through the wordlist? In that case you would also have to take into account when to delete an element from the set again. Alright, those were just some ideas or hints. There maybe a different way that you come up with. I hope the example input now makes the current issue a little clearer for you. Good luck! ;-)

Alex

Level 24 , Sibiu, Romania

16 January 2020, 18:33

For the moment I stepped over this task and I will come back later. Anyway, thank you for your tips. I will take them into consideration for this or further tasks. :D