Output matches, solution wrong?

Question about the task

Under discussion

I am lost. Am i just lucky the output matches the wanted output?🤨

Let's write a utility for working with arrays. The main functionality is ready: the printArray() method displays all the elements of the array on the console.
What is left for you is just a trifle: implement the reverseArray() method. It should reverse the order of the elements in the array.
The method should only work with arrays of integer values (int[]).

Example:
If the array contains the elements:
1, 2, 3, 4, 5, 6, 7, 8, 9, 0
then after calling the reverseArray() method it should contain:
0, 9, 8, 7, 6, 5, 4, 3, 2, 1

Requirements:

The reverseArray() method must reverse the order of the elements in the array.

package en.codegym.task.pro.task06.task0605; /* Correct order */ public class Solution { public static void main(String[] args) { int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}; printArray(array); reverseArray(array); printArray(array); } public static void reverseArray(int[] array) { for (int i= array.length - 1; i>=0; i--) { System.out.print(array[i] + ", "); } System.out.println(); } public static void printArray(int[] array) { for (int i : array) { System.out.print(i + ", "); } System.out.println(); } }

Comments (5)

Popular
New
Old

You must be signed in to leave a comment

Thomas

Level 41 , Bayreuth, Germany

30 January, 21:21

The task asks you to swap the elements inside the array and not to just output the array in reverse order. array index 0 1 2 .... 9 value before 1 2 3 .... 0 value after 0 9 8 .... 1

SadyWood

Level 10 , Norway

31 January, 09:13

i am confused on how to actually make it work. Solution that is provided feels like it could be better. any help on actually understanding how to solve?

Thomas

Level 41 , Bayreuth, Germany

31 January, 13:53

useful

That's not to difficult. Look at the above array.

int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};

To reverse this array with a length of 10 elements you first swap the values of indexes 0 and 9, then 1 and 8, 2 and 7.... 4 and 5 That's all. If you swap values you need to keep in mind that you can not do it directly like

array[9] = array[0];
array[0] = array[9];

I hope that's clear. After the first assignment both, index 9 and 0 would have the same value (the value of array[0]). Means you need to save the value of array[9] first in a temporary variable

int temp = array[9];
array[9] = array[0];
array[0] = temp;

This knowledge you add to a for loop and that's the entire magic:

public static void reverseArray(int[] array) {
    for (int i = 0; i < array.length / 2; i++) {
        int temp = array[array.length - i - 1];
        array[array.length - i - 1] = array[i];
        array[i] = temp;
    }
}

you even could move the swapping in its own method...

public static void reverseArray(int[] array) {
    for (int i = 0; i < array.length / 2; i++) {
        swap(array, i, array.length - i - 1);
    }
}

private static void swap(int[] array, int a, int b) {
    int temp = array[b];
    array[b] = array[a];
    array[a] = temp;
}

have fun coding ;)

SadyWood

Level 10 , Norway

31 January, 14:21

Thank you for the answer. I was still stuck in my head on why it needed to be divided by two in the for loop until I understood that leaving it without division would make it so the array that is printed out would be first reversed but then again put back into the original order. To prevent it from going back to the original order it is necessary to divide the length of loop steps.

janrembisch Software Architect

Expert

30 January, 21:01

yes indeed u are one lucky guy