Output as it supposed to be, but task won't get confirmed - as usually -,-

Question about the task

Shuffled just in time

Java Syntax, Level 7, Lesson 12

Under discussion

Where's the issue? Thanks alot.

package com.codegym.task.task07.task0720; import java.util.*; import java.io.IOException; import java.util.*; /* Checking the order */ public class Solution { public static void main(String[] args) throws IOException { Scanner s = new Scanner(System.in); ArrayList<String> list = new ArrayList<String>(); int N = s.nextInt(); int M = s.nextInt(); for (int i = 0; i <= N; i++) { list.add(s.nextLine()); } int num = 0; for (int i = 0; i < M; i++) { list.add(list.get(num+1)); list.remove(num+1); } for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

3 March 2020, 21:58

I see you figured this one out, here is a little explanation: https://stackoverflow.com/questions/13102045/scanner-is-skipping-nextline-after-using-next-or-nextfoo This explains that the nextInt() method of the scanner class does not consume new line characters (when you hit enter from the keyboard). It gathers the next available number from the input, whether is is on the same line or separate lines, completely ignoring white space. I see that you intuited this behavior by adjusting your code for the blank entry by making your for loop on line 22 go as long as "i <= N", and then shuffling the values from index 1 on and ignoring the blank entry at index 0. The problem is that you still output the blank line in the for loop on line 31 when you accessed index 0. It is important to realize this behavior in the Scanner class to avoid bugs.

Seb

Level 41 , Crefeld, Germany

1 March 2020, 09:54

Adjust your for-loop on line 22: If you start with i=0, then the condition needs to be i<N. If you start with i=1, then your condition can be i<=N. Adjust lines 27 and 28. The first element of a list is always element 0 - not element 1, thus line 27 should be list.add(list.get(0)); Change line 28 accordingly. That's it. ;-)

Art

Level 13 , Chisinau, Moldova, Republic of

1 March 2020, 10:14

I've done what you've said, still doesn't work and even makes it more inaccurate to the solution. My output on the existing code is what it supposed to be, try it.

Seb

Level 41 , Crefeld, Germany

1 March 2020, 10:50

Uiui, that's actually some strange scanner behaviour. Took me a moment to debug... :-) When you debug your for loop from line 22 as follows the strange scanner behaviour that has something to do with reading the next line will become apparent: for (int i = 0; i<=N; i++) { System.out.println("i: " + i); System.out.println("N: " + N); System.out.println("M: " + M); list.add(s.nextLine()); } Replace your scanner call from s.nextLine() on line 23 to just s.next(). The program will then work as I expected, and you will see that your program will not deliver the correct output. You can then procede with the adjustments I mentioned beforehand and it'll pass.

Seb

Level 41 , Crefeld, Germany

1 March 2020, 10:56

And here some sample data to test: N=5 M=2 Input: One Two Three Four Five Expected Output: Three Four Five One Two

Art

Level 13 , Chisinau, Moldova, Republic of

1 March 2020, 11:03

Mate I don't get 1 thing, if my output is correct in the first place, why any adjustments needed? What you've wrote still doesn't work and makes it worse ....

Seb

Level 41 , Crefeld, Germany

1 March 2020, 11:21

Sorry, for the confusion, but the issue is the call to s.nextLine(). I adjusted your code as follows and it works: Scanner s = new Scanner(System.in); ArrayList<String> list = new ArrayList<String>(); int N = s.nextInt(); int M = s.nextInt(); for (int i = 0; i < N; i++) { list.add(s.next()); } s.close(); for (int i = 0; i < M; i++) { list.add(list.get(0)); list.remove(0); } for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } Cheers Seb

Art

Level 13 , Chisinau, Moldova, Republic of

1 March 2020, 11:59

Yeah, same out put as I have received with my initial solution on the top of this page, no idea why your did go through and my didn't.

Seb

Level 41 , Crefeld, Germany

1 March 2020, 16:34

Yes, you're right - this program delivers the same output as your program did. And it may also not be apparent straight away why this one passes, and the other one didn't. Basically, the point is that the method s.nextLine() that you used in your program, created an unexpected program behaviour. The task requirement asked to move the first element from the list to the end, but your program moved the second element. When I ran your code and added the System.out.println("i: " + i) in the for loop as I put it in one of my above comments, I could see, that i is printed out twice instead of only once before the first call to s.nextLine(); I am not entirely sure why that is the case, but it has something to do with the s.nextLine() method. I too had tasks where my program created the expected output, but it only passed once I adjusted things around because the validation system sometimes expects certain things... ;-) This one was not easy to debug and you actually did a very good job. I hope I could help you at least a little bit - and wish you good luck for upcoming tasks and lessons.

Art

Level 13 , Chisinau, Moldova, Republic of

3 March 2020, 21:18

Thank you !!