Where is my mistake?

Question about the task

Longest sequence

Java Syntax, Level 8, Lesson 6

Under discussion

Hi, guys! Where is my mistake? Thank you in advance!

package com.codegym.task.task08.task0812;

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

/*
Longest sequence

*/

public class Solution {
    public static void main(String[] args) throws IOException {
        //write your code here
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        ArrayList<Integer> list = new ArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(Integer.parseInt(reader.readLine()));
        }

       int count = 1;

       int[] arr = new int[10];
       for (int i = 0; i < 9; i++) {
            if (list.get(i).equals(list.get(i+1))) {
                arr[i] = count;
                count++;
            }
        }

        int max = arr[0];
        for (int i = 0; i < 10; i++) {
            if (arr[i] > max) max = arr[i];
        }
        System.out.println(max);
    }
}

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; /* Longest sequence */ public class Solution { public static void main(String[] args) throws IOException { //write your code here BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); ArrayList<Integer> list = new ArrayList(); for (int i = 0; i < 10; i++) { list.add(Integer.parseInt(reader.readLine())); } int count = 1; int[] arr = new int[10]; for (int i = 0; i < 9; i++) { if (list.get(i).equals(list.get(i+1))) { arr[i] = count; count++; } } int max = arr[0]; for (int i = 0; i < 10; i++) { if (arr[i] > max) max = arr[i]; } System.out.println(max); } }

Comments (8)

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Nouser

Level 36 , Germany

9 December 2020, 11:46

There is more than one problem in your code. The showstopper probably is, that the counter doesn't reset when a new sequence starts. Means the if in line 24 needs a corresponding else clause. Here you set back count to 1. The next very small problem are lines 25, 26. You need to swap these. Otherwise, you save always the max sequence length before the counter increases to the true max. So your max will always be max - 1 If you're interested in some improvement of the code, then you could think about not using an array to save the actual sequence length but just a int variable that you use to hold the max. That will save the memory usage for the array and one loop to get the max.

Cristian

Level 13 , Ploiesti, Romania

11 December 2020, 16:07

Hi, Nouser! Thanks for clarification! Please, take me further! My new code is: package com.codegym.task.task08.task0812; import java.io.*; import java.util.ArrayList; /* Longest sequence */ public class Solution { public static void main(String[] args) throws IOException { //write your code here BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); ArrayList<Integer> list = new ArrayList(); for (int i = 0; i < 10; i++) { list.add(Integer.parseInt(reader.readLine())); } int count = 1; int[] arr = new int[10]; for (int i = 0; i < 9; i++) { if (list.get(i).equals(list.get(i+1))) { count++; arr[i] = count; } else { count = 1; } } int max = arr[0]; for (int i = 0; i < 10; i++) { if (arr[i] > max) max = arr[i]; } System.out.println(max); } } However, the last requirement is not fulfilled (The program should display the length of the longest sequence of repeating numbers in the list) Why? Thank you so much!

Nouser

Level 36 , Germany

11 December 2020, 16:21

With the suggested improvement, using a int max variable instead of an array your code probably would be working. Now there's another little problem that occurs when the max sequence is one. In that case arr[i] = count; never will get reached and therefore the array will stay at default values (0). Now you initialize max with int max = arr[0]; Means max is zero and it alway will be in the following loop where you try to grab the highest value. The output will be zero instead of 1. Should be fixed if you change max = arr[0]; to max = 1; Still I suggest to try the approach with int max. You'll need that later again.

Cristian

Level 13 , Ploiesti, Romania

11 December 2020, 16:49

Do you mean this way? package com.codegym.task.task08.task0812; import java.io.*; import java.util.ArrayList; /* Longest sequence */ public class Solution { public static void main(String[] args) throws IOException { //write your code here ArrayList<Integer> list = new ArrayList<Integer>(); BufferedReader reader = new BufferedReader(new InputStreamReader(System.in) ); int number = 0; int max = 1; int current = 1; for (int i = 0; i < 10; i++) { number = Integer.parseInt(reader.readLine()); list.add(number); } reader.close(); for (int i = 0; i < 9; i++) { if( list.get(i).equals(list.get(i+1))) { current ++; if (max < current) { max = current; } } else { current = 1; } } if (max < current) { max = current; } System.out.println(max); } }