Java, recursively reverse an array

Question

I haven\'t found anything with the specific needs of my function to do this, yes, it is for homework.

So I have:

public void reverseArray(int[] x) {
         


        

Answer 1

Because this is your homework, I suggest an example :

Given sequence : 1 2 3 4 5 6 7 8 9 10

You can change to : 10 2 3 4 5 6 7 8 9 1

After that: 10 9 3 4 5 6 7 8 2 1

.....

As you see, step by step, the sequence is "better" and the problem is "smaller". So, the problem you should solve to complete is :

1) How to apply recursive call for this method. for the original, the method is : reverse(int[] a). so, after first step, you should create array b from a[2] --> a[n-1]. and using reverse(int[] b)`.

2) after reverse b, what should we do to reverse a ? Assign values of b again back to a.

3) stop condition : what stop condition ? You see that elements of array b less than elements of array a. So, to which step, we should stop ?

Hope this help :)

Answer 2

This is probably the easiest way, not the fastest, but probably the easiest.

A whole program would look something like this:

public static void main(String [] args)
{
    BackwardsArray back = new BackwardsArray();
}

public BackwardsArray()
{
    int [] a = {1,2,3,4,5,6,7,8,9};
    printBackwards(a);
}

void printBackwards( int [] b)
{
    print(b,b.length-1);
}

void print(int [] b, int pos)
{
    System.out.println(b[pos]); // prints last item
    if(pos != 0)
    {
        print(b,pos-1);
    }
}

Hope it helps!

Answer 3

Here is the main method:

package main;

public class Main {
    public static void main(String[] args) {
        StringOps ops = new StringOps();
        String string = "Arjun";
        // reversing the string recrusively
        System.out.println(ops.reverseRecursively(string.toCharArray(), 0));
    }
}

and here is the recursive function:

package main;

public class StringOps {
    public char[] reverseRecursively(char[] array, int i) {
        char[] empty = new char[0];
        if (array.length < 1) {
            System.out.println("you entered empty string");
            return empty;
        }
        char temp;
        temp = array[i];
        array[i] = array[array.length - 1 - i];
        array[array.length - 1 - i] = temp;
        i++;

        if (i >= array.length - 1 - i) {
            return array;
        } else {
            reverseRecursively(array, i);
            return array;
        }

    }

}

Answer 4

public class FunWithAlgorthims {


public static void main(final String[] args) {

    String[] array = {"a", "b", "c", "d"};
    printArray(array);
    revereArrayRecusrive(array, 0);
    printArray(array);
}


public static void revereArrayRecusrive(final String[] array, int startPointer) {
    if (startPointer >= (array.length / 2)) {
        return;
    }
    String temp = array[startPointer];
    array[startPointer] = array[array.length - 1 - startPointer];
    array[array.length - 1 - startPointer] = temp;
    revereArrayRecusrive(array, ++startPointer);
}

public static void printArray(final String[] array) {
    Arrays.stream(array).forEach(a -> System.out.print(a + " "));
    System.out.println();
}

}

Answer 5

Calling reverseArray(0, n, arr) here n is length of array

public void reverseArray(int i, int n, int [] arr)
{
   if(i==n)
   {
     return ;
   } 
   else
   {
     reverseArray(i+1, n, arr);
     System.out.println(arr.at(i));
   }
}

Answer 6

private static void reversePrint(int[] numbers)
{
    if(numbers.length==0) {
        return;
    }
    int[] a = new int[numbers.length -1];
    for(int i =0;i<numbers.length-1;i++) {
        a[i] = numbers[i+1];
    }
    reversePrint(a);
    System.out.println(numbers[0]+" ");

}