Important Notice:

Practice-It will be discontinued as of November 1st, 2024. After this date, the website will remain online for a transitional period, but login will be restricted to University of Washington NetID authentication. This marks the next phase towards the platform's full retirement. Thank you for your use and support of the application over the years.

If you are looking for an alternative, a similar tool, CodeStepByStep, was developed independently by the original author of Practice-It, and is available at codestepbystep.com**

logo Practice-It logo

Main Page → Problems → Solve a Problem

collapse

Related Links:
Author: Stuart Reges (on 2014/02/13)

Write a method collapse that collapses a list of integers by replacing each successive pair of integers with the sum of the pair. For example, if a variable called list stores this sequence: 

    [7, 2, 8, 9, 4, 13, 7, 1, 9, 10]

and the following call is made: 

    list.collapse();

The first pair should be collapsed into 9 (7 + 2), the second pair should be collapsed into 17 (8 + 9), the third pair should be collapsed into 17 (4 + 13) and so on to yield: 

    [9, 17, 17, 8, 19]

If the list stores an odd number of elements, the final element is not collapsed. For example, the sequence: 

    [1, 2, 3, 4, 5]

would collapse into: 

    [3, 7, 5]

You are writing a method for the ArrayIntList class discussed in lecture: 

    public class ArrayIntList {
        private int[] elementData; // list of integers
        private int size;          // current # of elements in the list

        <methods>
    }

You are not to call any other ArrayIntList methods to solve this problem, you are not allowed to define any auxiliary data structures (no array, ArrayList, etc), and your solution must run in O(n) time where n is the length of the list to be collapsed.

Type your solution here:


This is a partial class problem. Submit code that will become part of an existing Java class as described. You do not need to write the complete class, just the portion described in the problem.

You must log in before you can solve this problem.


Log In

If you do not understand how to solve a problem or why your solution doesn't work, please contact your TA or instructor.
If something seems wrong with the site (errors, slow performance, incorrect problems/tests, etc.), please

Is there a problem? Contact a site administrator.