CodeGym/Hilfe mit Java-Aufgaben/Where is the problem?

Level 34

Aachen

07.06.2023
334Aufrufe
11Kommentare

Where is the problem?

Frage zur Aufgabe

In der Diskussion

Hi there, on the mentor's recommendation, I should try the words in the task description, but I get exactly the same result with them. If no complete word chain can be formed, an empty StringBuilder is returned - this also corresponds to the sample solution. Nevertheless the validation does not want to work. Regards.

In the main method, read the name of a file that contains words separated by spaces from the console.
In the getLine method, use StringBuilder to order all the words as follows: the last letter of a word must match the first letter of the next word (ignore case).
Each word should be used once.
The getLine method can return any variant.
Separate words with a space.
Display the resulting string on the screen.

Example input file:

Okinawa Washington Auckland Kalamazoo Norfolk

Result:

Washington Norfolk Kalamazoo Okinawa Auckland

Anforderungen:

The main method must read the filename from the keyboard.
There should not be static fields in the Solution class.
The getLine method must use StringBuilder.
The getLine method must return an empty string (an empty StringBuilder) if it is not passed arguments (words).
The getLine method must not change the arguments (words).
All words passed to the getLine method must be included in the resulting string, if possible.
The screen output must match the task conditions.

package com.codegym.task.task22.task2209; /* Make a word chain */ import java.io.BufferedReader; import java.io.FileReader; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.Arrays; public class Solution { public static void main(String[] args) { String fileName = null; String[] words; StringBuilder sb = null; try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) { fileName = br.readLine(); } catch (Exception e) {e.printStackTrace();} try (BufferedReader br = new BufferedReader(new FileReader(fileName))) { StringBuilder content = new StringBuilder(); while (br.ready()) content.append(br.readLine()+" "); words = content.toString().trim().split("\\s+"); sb = getLine(words); } catch (Exception e) {e.printStackTrace();} System.out.println(sb); } public static StringBuilder getLine(String... words) { StringBuilder sb = new StringBuilder(); Word.AddWords(words); boolean start=false, end=false; while (Word.words.size() > 0) { Word item = Word.words.get(0); Word.words.remove(0); Word prev=Word.getPrevious(item); Word next=Word.getNext(item); int offset = sb.length(); if (prev == null) { if (start) return new StringBuilder(); else { start = true; offset = 0; } } else if (!Word.words.contains(prev)) { offset = sb.indexOf(prev.text)+prev.text.length(); } if (next == null) { if (end) return new StringBuilder(); else end=true; } else if (!Word.words.contains(next)) { offset = sb.indexOf(next.text)-1; } sb.insert(offset,(offset == 0 && start) ? item.text : " "+item.text); } return sb; } private static class Word { private static ArrayList<Word> init = new ArrayList(); private static ArrayList<Word> words = new ArrayList(); final String text; final char start, end; private Word(String text) { this.text = text; this.start = text.toLowerCase().charAt(0); this.end = text.toLowerCase().charAt(text.length()-1); init.add(this); words.add(this); } public static void AddWords(String... words) { for (String word : words) new Word(word); } public static Word getNext(Word word) { for (Word w : init) { if (w == word) continue; if (word.end == w.start) return w; } return null; } public static Word getPrevious(Word word) { for (Word w : init) { if (w == word) continue; if (word.start == w.end) return w; } return null; } public String toString() {return text;} } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 14:15

nützlich

I tried the code with the words: Pet Tough shift and nothing was output. There is a lot going on in this code and I haven't had time to really break it down, but did find that with my example, there must be a bug somewhere as those three words should at least have a two word output. The task does say that any complete chain is acceptable output. Say if you had the words: Pet Tough shift tiffany Either the chains: Pet Tough or Pet tiffany or shift tiffany or shift tough would pass the task (not just the longest chain) as they are complete chains that exist in the words given.

Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 14:28

When we were first doing this task we thought that we had to output the longest chain that existed in the words, which made coding this task a lot more complicated. We figured out that they just wanted any complete chain. (I say we because there were about 10 of us that used to talk on discord when the multithreading questline went live and we were doing the tasks about the same pace). I can describe the logic of my code that passed the task: **After reading the words from the file and passing to the getLine() method** 1) go through each word until you find two that fit together to start the chain 2) for each word left in the list of words **do the first of a, b, or c that is true** a) put it at front of the chain if it fits in the front b) check in between each word and put it in the middle of the chain if it can fit c) put it at the end of the chain if it can fit and remember to remove or mark each word as it is used. That pretty much sums up my entire logic.

TK87

Level 34 , Aachen, Germany

7 Juni 2023, 14:34

But when I try your words in the sample solution, I also get no output. For me it seems, as only then something should be output at all, if really all words in the list can also be formed to a chain.

TK87

Level 34 , Aachen, Germany

7 Juni 2023, 14:50

No, unfortunately this does not work. In my code you only need to replace "return new StringBuilder();" with "continue;" in lines 47 & 56. Then add the following line below line 42 and everything works exactly as you described:

if (prev == null && next == null) continue;

Unfortunately, the validation still fails.

Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 15:05

"But when I try your words in the sample solution, I also get no output." Correct output would be: Pet Tough or shift Tough

Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 15:07

It says that: All words passed to the getLine method must be included in the resulting string, if possible. That means that if it is not possible then you still have to output a chain if one exists.

Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 15:13

You have to ensure that when you add a word to the chain that you check ALL the words that are still left in the list of unused words. Say, for example, that you have the words: Just marble exam time something If you started the chain with Just time, then test marble and find it doesn't fit in that chain, move to test exam and find it fits at the end so you now have Just time exam, you need to make sure your code goes back to marble because it now fits in the chain at the end of exam. So the correct answer to those words would be: Just time exam marble

TK87

Level 34 , Aachen, Germany

7 Juni 2023, 16:01

"Correct output would be: Pet Tough" No, that is not true. Go to the Task and download the correct solution. If you enter these words there, you will not get any output either. In addition, if you make the changes I described above, you get the output you described - but the validation fails.

Guadalupe Gagnon

Level 37 , Tampa, United States

7 Juni 2023, 16:28

The conditions specifically state: "The getLine method can return any variant." I still have my code that passed and it outputs: shift Tough

Guadalupe Gagnon

Level 37 , Tampa, United States

8 Juni 2023, 13:34

After a night and testing your code a little more I have found a potential issues: A lot of people run into this issue in tasks by using static variables when they are not needed. The problem is that getLine() can be called multiple times, however in the above code this will cause an error as the static lists the code uses, init and words of the Word class, are already filled when the method is called after the first time. Take this example:

public static void main(String[] args) {
   System.out.println(getLine("Okinawa Washington Auckland Kalamazoo Norfolk".split(" ")));
   System.out.println(getLine("Okinawa Washington Auckland Kalamazoo Norfolk".split(" ")));
}

It should output the words ordered according to the task 2 times, however after the first time it orders and prints out the words it crashes with a StringIndexOutOfboundsException. You can probably fix this by simply clearing those static lists at the very start of the getLine() method to ensure that any new values passed to it are calculated properly.

TK87

Level 34 , Aachen, Germany

12 Juni 2023, 05:35

Thanks, I have changed it. Unfortunately, the validation still fails.