ShellSort.java

public class ShellSort {
    public static <T extends Comparable<? super T>> void shellSort(T[] array, int start, int end) {
        int numEntries = end - start + 1;
        int space = numEntries/2;

        while (space > 0) {
            System.out.println("Starting shellSort, space is: " + space);
            for (int i = start; i < start + space; i++) {
                incrementalInsertionSort(array, i, end, space);
            }
            space /= 2;
            System.out.println("After for loop, space is: " + space);
        }
    }

    private static <T extends Comparable<? super T>> void incrementalInsertionSort(T[] array, int start, int end, int space) {
        int unsorted;
        int index;

        for (unsorted = start; unsorted <= end; unsorted += space) {
            T nextInsert = array[unsorted];
            index = unsorted - space;

            while ((index >= start) && (nextInsert.compareTo(array[index]) < 0)) {
                array[index + space] = array[index];
                index -= space;
                System.out.println("In incrementalInsertionSort while loop");
                SortingDriver.displayCurrent(array);
            }

            array[index + space] = nextInsert;
            System.out.println("In incrementalInsertionSort outside while loop");
            SortingDriver.displayCurrent(array);
        }
    }
}