CodeGym/Help with Java Tasks/What is wrong here?

Level 26

Zagreb

19.03.2019
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9comments

What is wrong here?

Question about the task

Resolved

package com.codegym.task.task08.task0812;

import java.io.*;
import java.util.ArrayList;
import java.util.Collections;

/*
Longest sequence

*/
public class Solution {
    public static void main(String[] args) throws IOException {
        //write your code here
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        ArrayList<Integer> list = new ArrayList<>();

        for (int i = 0; i < 10; i++) {
            Integer n = Integer.parseInt(br.readLine());
            list.add(n);
        }




        int counterA = 1;
        int counterB = 0;

        for (int i = 0; i < list.size()-1; i++) {
            if (list.get(i).equals(list.get(i + 1)))
                counterA++;

            else if (counterA > counterB) {
                counterB =+ counterA;

                counterA = 1;
            }

        }

        if (counterA > counterB) {
            counterB = counterA;

        }
        System.out.println(counterB);

    }

}

1. Create a list of numbers.
2. Use the keyboard to add 10 numbers to the list.
3. Display the length of the longest sequence of repeating numbers in the list.

Example for the list 2, 4, 4, 4, 8, 8, 4, 12, 12, 14:
3

The value is 3, because the longest sequence of repeating numbers is three fours.

Requirements:

The program must display a number on the screen.
The program should read values from the keyboard.
In the main method, declare an ArrayList variable with Integer elements and immediately initialize it.
The program should add 10 numbers to the collection in accordance with the conditions.
The program should display the length of the longest sequence of repeating numbers in the list.

package com.codegym.task.task08.task0812; import java.io.*; import java.util.ArrayList; import java.util.Collections; /* Longest sequence */ public class Solution { public static void main(String[] args) throws IOException { //write your code here BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); ArrayList<Integer> list = new ArrayList<>(); for (int i = 0; i < 10; i++) { Integer n = Integer.parseInt(br.readLine()); list.add(n); } int counterA = 1; int counterB = 0; for (int i = 0; i < list.size()-1; i++) { if (list.get(i) == (list.get(i + 1))) counterA++; if (counterA > counterB) { counterB = counterA; counterA = 1; } } System.out.println(counterB); } }

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Mateo

Level 26 , Zagreb, Croatia

19 March 2019, 18:37

solution

Thank you so much Guadalupe, got it right in my head after i read your comment! this is the solution

package com.codegym.task.task08.task0812;

import java.io.*;
import java.util.ArrayList;
import java.util.Collections;

/*
Longest sequence

*/
public class Solution {
    public static void main(String[] args) throws IOException {
        //write your code here
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //In the main method, declare an ArrayList variable with Integer elements and immediately initialize it.
        ArrayList<Integer> list = new ArrayList<>();

        // inserting 10 numbers into list
        for (int i = 0; i < 10; i++) {
            Integer n = Integer.parseInt(br.readLine());
            list.add(n);
        }


        int counterA = 1;       // counter set to 1 (we start counting sequence at 1)
        int counterB = 0;       // in this variable we later save longest sequence

        for (int i = 0; i < list.size()-1; i++) {    // repeat until list.size() - 1 because in next line we get numbers from current index i + 1
            if (list.get(i).equals(list.get(i + 1))) // use equals for numbers > 127
                counterA++;                          //if 2 numbers are in sequence increase counter by 1
            else {
                    if (counterA >= counterB)       // check if current sequence is bigger than last
                    counterB = counterA;            // save the biggest sequence in variable counterB
                    counterA = 1;                   // reset the counter

            }



        }

        if (counterA>counterB) {   //we put this statement to check if last numbers from the list are in the biggest sequence ( because in if statement above you don't save it in counterB variable)
            counterB = counterA;

        }

        System.out.println(counterB);

    }

}

Bazsó Benjámin

Level 20 , Szombathely, Hungary

28 March 2019, 16:27

for (int i = 0; i < list.size()-1; i++)

why do we have to write list.size()-1 instead of just list.size()?

Mateo

Level 26 , Zagreb, Croatia

28 March 2019, 16:36

Because in the next line

if (list.get(i).equals(list.get(i + 1)))

it checks if numbers are in sequence. So if you don't put list.size()-1 the program will crash because it will try to check for next number when he already is at last position in a list.

Picvajzmen

Level 20 , Belgrade, Serbia

15 May 2019, 07:23

I think it is because of this line that comes after - if (list.get(i).equals(list.get(i + 1)))

MBC

Level 14 , Apeldoorn, Netherlands

8 July 2019, 11:52

What is the 127 for?

Mateo

Level 26 , Zagreb, Croatia

9 July 2019, 15:58

If you are referring to the comment in line 30, when using == for wrapper classes (Integer), for numbers greater than 127, this way you will compare references and not values, so will return false (128 == 128 or greater -> false) read more: stackoverflow autoboxing-explained

MBC

Level 14 , Apeldoorn, Netherlands

10 July 2019, 13:03

Thanks

Vahan

Level 41 , Tbilisi, Georgia

16 July 2019, 08:06

Nice model to learn java thinking

Guadalupe Gagnon

Level 37 , Tampa, United States

19 March 2019, 17:50

useful

It is because of the way your if statements are. Every time there is a match it increases A no matter if the match is in sequence or not. Then every loop cycle it checks if A is greater than B, when it is it changes B to A then sets A to one. Try entering all the same numbers, like all 1's. The output should be ten, but your code outputs 4. Here is a step through of your code when 10 1's are entered: Loop cycle 1 - checking 1 against 1 Match! A = 2 A is greater than B - B set to 2: A set to 1 Loop cycle 2 - checking 1 against 1 Match! A = 2 Loop cycle 3 - checking 1 against 1 Match! A = 3 A is greater than B - B set to 3: A set to 1 Loop cycle 4 - checking 1 against 1 Match! A = 2 Loop cycle 5 - checking 1 against 1 Match! A = 3 Loop cycle 6 - checking 1 against 1 Match! A = 4 A is greater than B - B set to 4: A set to 1 Loop cycle 7 - checking 1 against 1 Match! A = 2 Loop cycle 8 - checking 1 against 1 Match! A = 3 Loop cycle 9 - checking 1 against 1 Match! A = 4 Program output: "4"