how do you pass the last 2 validations?

Question about the task

Make a word chain

Java Multithreading, Level 2, Lesson 9

Under discussion

My output for "Okinawa Washington Auckland Kalamazoo Norfolk" is "Washington Norfolk Kalamazoo Okinawa Auckland"

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.*; import java.util.*; public class Solution { public static void main(String[] args) throws IOException { List<String> words = new ArrayList<>(); try (BufferedReader buff = new BufferedReader(new InputStreamReader(System.in)); BufferedReader read = new BufferedReader(new FileReader(buff.readLine()))) { while (read.ready()) words.addAll(Arrays.asList(read.readLine().split("\\s+"))); } StringBuilder result = getLine(words.toArray(new String[0])); System.out.println(result.toString()); } public static StringBuilder getLine(String... words) { if (words.length < 1) return new StringBuilder(); List<String> wordList = new ArrayList<>(Arrays.asList(words)); Set<Character> set = new HashSet<>(); StringBuilder sb = new StringBuilder(); wordList.forEach(f -> set.add(f.toLowerCase().charAt(f.length() - 1))); for (String word : words) { if (!set.contains(word.toLowerCase().charAt(0))) { sb.append(word); wordList.remove(word); break; } } for (int i = 0; i < wordList.size(); ++i) { String s = wordList.get(i); if (s.toLowerCase().charAt(0) == sb.charAt(sb.length() - 1)) { sb.append(" ").append(s); wordList.remove(s); i = -1; } } return wordList.size() > 0 ? new StringBuilder() : sb; } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

9 November 2020, 17:44

The problem is that this code should return any valid chain of words. Take for example the words: Okinawa Washington Zuckland Kalamazoo Norfolk (where I changed Auckland to Zuckland) Because "Zuckland" would remain in the wordList at the end of the algorithm, line 44 would return a blank StringBuilder. A correct return would be still be: Washington Norfolk Kalamazoo Okinawa

Guadalupe Gagnon

Level 37 , Tampa, United States

9 November 2020, 17:56

I should mention also that in my above example if your code returned: Zuckland that would also be a correct answer as any variation would pass.

Ian De Bie Full Stack Developer

9 November 2020, 18:04

i adjusted my code and my output for "Okinawa Washington Zuckland Kalamazoo Norfolk" is now Washington Norfolk Kalamazoo Okinawa, but it still doesn't pass the last two validations for some reason

public static StringBuilder getLine(String... words) {
    StringBuilder sb = new StringBuilder();

    if (words.length < 1) return sb;
    else if (words.length == 1) {
        sb.append(words[0]);
        return sb;
    }

    List<String> wordList = new ArrayList<>(Arrays.asList(words));
    Set<Character> set = new HashSet<>();
    wordList.forEach(f -> set.add(f.toLowerCase().charAt(f.length() - 1)));
    for (String word : words) {
        if (!set.contains(word.toLowerCase().charAt(0))) {
            sb.append(word);
            wordList.remove(word);
            break;
        }
    }

    for (int i = 0; i < wordList.size(); ++i) {
        String s = wordList.get(i);
        if (s.toLowerCase().charAt(0) == sb.charAt(sb.length() - 1)) {
            sb.append(" ").append(s);
            wordList.remove(s);
            i = -1;
        }
    }

    return sb;
}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 November 2020, 18:53

Line 23 is throwing a String index out of bounds exception for index -1 when I test it with values: Dunk Altoid Kayla This is occurring because the loop at line 13 is trying to attempt to find a start word, but this list has a circular reference and no start word is entered into sb. Because sb is blank for line 23, there is no char at the length - 1. In this example case the correct answers would be: Dunk Kayla Altoid or Altoid Dunk Kayla

Ian De Bie Full Stack Developer

9 November 2020, 21:46

you're so good at finding bugs, thanks for pointing that one out. now i have fixed that one, so my output for "Dunk Altoid Kayla" is "Dunk Kayla Altoid", but i still fail validation. revised code:

public static StringBuilder getLine(String... words) {
    StringBuilder sb = new StringBuilder();
    if (words.length < 1) return sb;

    List<String> wordList = new ArrayList<>(Arrays.asList(words));
    Set<Character> set = new HashSet<>();
    wordList.forEach(f -> set.add(f.toLowerCase().charAt(f.length() - 1)));

    for (String word : wordList) {
        if (!set.contains(word.toLowerCase().charAt(0))) {
            sb.append(word);
            wordList.remove(word);
            break;
        }
    }

    if (sb.length() < 1) {
        sb.append(wordList.get(0));
        wordList.remove(0);
    }

    for (int i = 0; i < wordList.size(); ++i) {
        String s = wordList.get(i);
        if (s.toLowerCase().charAt(0) == sb.charAt(sb.length() - 1)) {
            sb.append(" ").append(s);
            wordList.remove(s);
            i = -1;
        }
    }

    return sb;
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 November 2020, 04:03

You're going to hate me... but take, for example, this: Altoid Dianne Dunk Kayla The returned value was: Altoid Dianne However correct returns would be Dunk Kayla Altoid Dianne // values can be added in front so would fail the part about everything being used if possible or Altoid Dunk Kayla // still a valid alternative

Guadalupe Gagnon

Level 37 , Tampa, United States

10 November 2020, 04:06

I solved this originally with brute force by checking each word and then building every single chain possible. Then it would check the size of each chain and return the one that was the largest. You don't need to do all that, as long as you can make it so every single word is considered for both the front and back of the chain.

Ian De Bie Full Stack Developer

10 November 2020, 05:12

ahh, i see what you mean. i'll have to consider a new algorithm. thanks for pointing out this edge case, very helpful.

Ian De Bie Full Stack Developer

3 September 2022, 21:47

finally passed after getting some recursion ideas from other solutions my passing solution