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My code works for the task example. I would have expected it to fail: All words passed to the getLine method must be included in the resulting string, if possible. as if there is a word that doesn't fit in with the word chain, I would have an infinite loop. I especially don't understand why it's failing: The getLine method must return an empty string (an empty StringBuilder) if it is not passed arguments (words)

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

Requirements:

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; public class Solution { public static void main(String[] args) throws Exception{ // ... BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String fileName = reader.readLine(); BufferedReader bufferedReader = new BufferedReader(new FileReader(fileName)); String chain = bufferedReader.readLine(); String[] words = chain.split(" "); StringBuilder result = getLine(words); System.out.println(result.toString()); } public static StringBuilder getLine(String... words) { StringBuilder chain = new StringBuilder(""); if (words == null) return chain; ArrayList<String> wordList = new ArrayList<>(); wordList.add(words[0]); while (wordList.size() < words.length){ for (int i = 0; i < wordList.size(); i++){ for (int j = 1; j < words.length; j++){ if (wordList.contains(words[j])) continue; if (checkEndings(wordList.get(i), words[j])) wordList.add(i, words[j]); else if (checkEndings(words[j], wordList.get(i))) wordList.add(i+1, words[j]); } } } for (String s : wordList) chain.append(s).append(" "); chain.deleteCharAt(chain.length()-1); return chain; } public static boolean checkEndings(String a, String b){ return String.valueOf(a.charAt(0)).equalsIgnoreCase(String.valueOf(b.charAt(b.length()-1))) ; } }

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Abhilash Sunariwal

Level 41 , Ajmer, India

17 February 2021, 00:46

useful

Line 20 : You are only reading single line from the file. It is possible that file contains more than one line. Line 31 : Add new line to return an empty StringBuilder if words.length==0.

Anthony Chalk

Level 30 , London, United Kingdom

17 February 2021, 09:04

Thank you, my code is now:

public class Solution {
    public static void main(String[] args) throws Exception{
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String fileName = reader.readLine();
        BufferedReader bufferedReader = new BufferedReader(new FileReader(fileName));
        ArrayList<String> wordList = new ArrayList<>();
        String word;
        while ((word = bufferedReader.readLine()) != null){
            String[] split = word.split(" ");
            for (String s: split)
                wordList.add(s);
        }
        String[] words = new String[wordList.size()];
        words = wordList.toArray(words);
        StringBuilder result = getLine(words);
        System.out.println(result.toString());
    }

    public static StringBuilder getLine(String... words) {
        StringBuilder chain = new StringBuilder("");
        if (words == null || words.length == 0) return chain;

        ArrayList<String> wordList = new ArrayList<>();
        wordList.add(words[0]);

        while (wordList.size()  < words.length){
            for (int i = 0; i < wordList.size(); i++){
                for (int j = 1; j < words.length; j++){
                    if (wordList.contains(words[j])) continue;
                    if (checkEndings(wordList.get(i), words[j]))
                        wordList.add(i, words[j]);
                    else if (checkEndings(words[j], wordList.get(i)))
                        wordList.add(i+1, words[j]);
                }
            }
        }

        for (String s : wordList)
            chain.append(s).append(" ");
        chain.deleteCharAt(chain.length()-1);
        return chain;
    }

    public static boolean checkEndings(String a, String b){
        return String.valueOf(a.charAt(0)).equalsIgnoreCase(String.valueOf(b.charAt(b.length()-1))) ;
    }
}

it still fails the last condition

Nouser

Level 36 , Germany

17 February 2021, 12:11

solution

try Okinawa Kalamazoo Auckland dread dare when executing wordList.add(position, word) there is a possibility, the position is in between already added words. So you interrupt your already found chain. Easy fix would be to check if i is at the beginning of the list or i + 1 at the end before adding a word to wordList. Very good solution btw.

Anthony Chalk

Level 30 , London, United Kingdom

17 February 2021, 12:37

Thanks very much

Vitali Kalaskou

Level 31 , Novopolotsk, Belarus

13 April 2022, 20:06

Passed the validation with your help. But when I try "Osaka Okinawa Washington Auckland Kalamazoo Norfolk" as input string I get an infinite running program.

Lisa L

Level 47 , Nuremberg, Germany

16 April 2022, 08:53

don't know if it validates but it gives a result for your input, it even does more than the tasks asks for and returns one of the best matches (if there are several) not any match.

public static void main(String[] args) {
    String[] words;
    try (BufferedReader console = new BufferedReader(new InputStreamReader(System.in))) {
        words = Files.lines(Paths.get(console.readLine()))
                .flatMap(line -> Stream.of(line.split("\\s+")))
                .toArray(String[]::new);
    } catch (IOException ioe) {
        throw new RuntimeException(ioe);
    }
    System.out.println(getLine(words));
}

public static StringBuilder getLine(String... words) {
    TreeSet<String> allPossibilities = recurse(new ArrayList<>(Arrays.asList(words)),
            new TreeSet<>(Comparator.comparing(String::length).reversed()), "");

    return allPossibilities.isEmpty() ? new StringBuilder() :
            new StringBuilder(allPossibilities.stream().limit(1).findFirst().get());
}

public static TreeSet<String> recurse(List<String> words, TreeSet<String> result, String root) {
    for (int i = 0; i < words.size(); i++) {
        String currWord = words.get(i);
        if (!root.isEmpty()) {
            if (!matches(root, currWord))
                continue;
        }
        String newRoot = root.isEmpty() ? currWord : root + " " + currWord;

        result.add(newRoot);

        if (words.size() > 1) {
            List<String> recList = new ArrayList<>(words);
            recList.remove(i);
            recurse(recList, result, newRoot);
        }
    }
    return result;
}

public static boolean matches(String a, String b) {
    return a.toLowerCase().charAt(a.length() - 1) == b.toLowerCase().charAt(0);
}