refactor: cleanup ShellSort (#5302)

This commit is contained in:
Alex Klymenko
2024-07-26 09:55:11 +03:00
committed by GitHub
parent ebed8b38b8
commit 5113101e5d
2 changed files with 51 additions and 86 deletions

View File

@ -11,36 +11,59 @@ public class ShellSort implements SortAlgorithm {
*/
@Override
public <T extends Comparable<T>> T[] sort(T[] array) {
int length = array.length;
int gap = 1;
/* Calculate gap for optimization purpose */
while (gap < length / 3) {
gap = 3 * gap + 1;
if (array.length == 0) {
return array;
}
for (; gap > 0; gap /= 3) {
for (int i = gap; i < length; i++) {
int j;
T temp = array[i];
for (j = i; j >= gap && SortUtils.less(temp, array[j - gap]); j -= gap) {
array[j] = array[j - gap];
}
array[j] = temp;
}
int gap = calculateInitialGap(array.length);
while (gap > 0) {
performGapInsertionSort(array, gap);
gap = calculateNextGap(gap);
}
return array;
}
/* Driver Code */
public static void main(String[] args) {
Integer[] toSort = {4, 23, 6, 78, 1, 54, 231, 9, 12};
ShellSort sort = new ShellSort();
sort.sort(toSort);
for (int i = 0; i < toSort.length - 1; ++i) {
assert toSort[i] <= toSort[i + 1];
/**
* Calculates the initial gap value using the Knuth sequence.
*
* @param length the length of the array.
* @return the initial gap value.
*/
private int calculateInitialGap(final int length) {
int gap = 1;
while (gap < length / 3) {
gap = 3 * gap + 1;
}
return gap;
}
/**
* Calculates the next gap value.
*
* @param currentGap the current gap value.
* @return the next gap value.
*/
private int calculateNextGap(final int currentGap) {
return currentGap / 3;
}
/**
* Performs an insertion sort for the specified gap value.
*
* @param array the array to be sorted.
* @param gap the current gap value.
* @param <T> the type of elements in the array.
*/
private <T extends Comparable<T>> void performGapInsertionSort(final T[] array, final int gap) {
for (int i = gap; i < array.length; i++) {
T temp = array[i];
int j;
for (j = i; j >= gap && SortUtils.less(temp, array[j - gap]); j -= gap) {
array[j] = array[j - gap];
}
array[j] = temp;
}
SortUtils.print(toSort);
}
}