Java: Interleaving multiple arrays into a single array

Question

I found similar question about interleaving two arraylists into one, but its in PHP. I was asked this question in interview as well but could\'nt solve it, came back to SO t

Answer 1

The lists don't have to be the same size:

public class InterleaveTwoLists {

    public List interleaveLists(final List first, final List second) {

        return new AbstractList() {
            private int minSize;
            private int combinedMinSize;
            private int size;
            private ListlargerList;
            {{
                minSize = Math.min(first.size(), second.size());
                combinedMinSize = minSize*2;
                size = first.size() + second.size();
                largerList = first.size() > minSize ? first : second;
            }}

            public int size() {
                return size;
            }

            public X get(int index) {
                if (index < combinedMinSize) {
                    return index % 2 == 0 
                        ? first.get(index / 2) 
                        : second.get(index / 2);
                }
                else { 
                    return largerList.get(index-minSize);
                }
            }
        };
    }
}

To test this:

public class InterleaveTwoListsTest {

    private static final Logger log = 
        LoggerFactory.getLogger(InterleaveTwoListsTest.class);

    List first = new ArrayList() {
    { 
        add("one"); add("three"); add("five"); 
        add("seven"); add("eight"); add("nine");
    }};

    List second = new ArrayList() {
    { 
        add("two"); add("four"); add("six"); 
    }};


    private InterleaveTwoLists interleaveTwoLists;

    @Before
    public void setUp() throws Exception {
        interleaveTwoLists = new InterleaveTwoLists<>();
    }

    @Test
    public void test() {
        List combinedList = interleaveTwoLists.interleaveLists(first, second);
        for( int i = 0; i < first.size() + second.size(); i++) { 
            log.debug("{}: {}", i, combinedList.get(i));
        }
    }
}