Recursively reverse an array of strings

Question

Create and return a new array that is a reversed copy of the array passed as a parameter.

The code I have is the following. I am stuck on the algorithm? This was an exam question but the exam is now over.

import java.util.*;

public class Q4_ArrayReverse
{
   public static String[] reverse( String[] in )
   {
      String[] out = new String[ in.length ];
      reverse( in, out, 0 );
      return out;
   }
   ///////////////////////////////////////////////////////////
   //
   // Given an input array, an output array and an index,
   //    copy the element at the index offset of the input array
   //    to the appropriate reversed position in the output array.
   //    i.e. in[ 0 ] -> out[ n - 1 ]
   //         in[ 1 ] => out[ n - 2 ]
   //            etc.
   //    After doing the copy for index, recurse for index + 1
   //    Be sure to quit when you get to the end of the array.
   //
   //////////////////////////////////////////////////////////
   static void reverse( String[] in, String[] out, int index )
   {







   }

Well, break it down into its components. In recursion, there always needs to be a terminating condition. — OldProgrammer
– OldProgrammer, Commented Apr 25, 2013 at 23:36
Q4_ArrayReverse is a hateful class name that doesn't match the Java naming convention. — Lion
– Lion, Commented Apr 25, 2013 at 23:37

arshajii · Accepted Answer · 2013-04-25 23:34:41Z

1

In your second (currently blank) method, you will want to swap elements at indexes index and in.length - index - 1 when putting them in the new out array. Then of course you want to do the same for index + 1, unless you are at the middle of the array in which case you're finished and can return.

if (index == array.length / 2)  // i.e. 1 position past the middle
    return

out[index] = in[in.length - index - 1];
out[in.length - index - 1] = in[index];

reverse(in, out, index+1);

answered Apr 25, 2013 at 23:34

arshajii

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codeAligned Over a year ago

if (index == in.length) // i.e. 1 position past the middle return; out[out.length - (index + 1)] = in[index]; reverse(in, out, index+1); It turns out this was enough, not sure why array.length/2 is not necessary.

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