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Merged
siriak merged 2 commits into from
Jul 26, 2024
+50 −85
Merged

refactor: cleanup ShellSort #5302

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df2e79f
refactor: ShellSort refactoring, improving test according to general …
Jul 25, 2024
0d17676
checkstyle: remove redundant line
Jul 25, 2024
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refactor: ShellSort refactoring, improving test according to general … 
…approach
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Alex Klymenko
Alex Klymenko committed Jul 25, 2024
commit df2e79f4f57e47e07826c923138ac10bfbaec488
70 changes: 47 additions & 23 deletions src/main/java/com/thealgorithms/sorts/ShellSort.java
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Original file line number Diff line number Diff line change
Expand Up @@ -11,36 +11,60 @@ 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};
/**
* 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;
}

ShellSort sort = new ShellSort();
sort.sort(toSort);
for (int i = 0; i < toSort.length - 1; ++i) {
assert toSort[i] <= toSort[i + 1];
/**
* 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);
}

}
66 changes: 4 additions & 62 deletions src/test/java/com/thealgorithms/sorts/ShellSortTest.java
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@@ -1,66 +1,8 @@
package com.thealgorithms.sorts;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;

import org.junit.jupiter.api.Test;

public class ShellSortTest {

private ShellSort shellSort = new ShellSort();

@Test
public void shellSortEmptyArray() {
Integer[] inputArray = {};
Integer[] outputArray = shellSort.sort(inputArray);
Integer[] expectedOutput = {};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortSingleIntegerArray() {
Integer[] inputArray = {4};
Integer[] outputArray = shellSort.sort(inputArray);
Integer[] expectedOutput = {4};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortSingleStringArray() {
String[] inputArray = {"s"};
String[] outputArray = shellSort.sort(inputArray);
String[] expectedOutput = {"s"};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortNonDuplicateIntegerArray() {
Integer[] inputArray = {6, -1, 99, 27, -15, 23, -36};
Integer[] outputArray = shellSort.sort(inputArray);
Integer[] expectedOutput = {-36, -15, -1, 6, 23, 27, 99};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortDuplicateIntegerArray() {
Integer[] inputArray = {6, -1, 27, -15, 23, 27, -36, 23};
Integer[] outputArray = shellSort.sort(inputArray);
Integer[] expectedOutput = {-36, -15, -1, 6, 23, 23, 27, 27};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortNonDuplicateStringArray() {
String[] inputArray = {"s", "b", "k", "a", "d", "c", "h"};
String[] outputArray = shellSort.sort(inputArray);
String[] expectedOutput = {"a", "b", "c", "d", "h", "k", "s"};
assertArrayEquals(outputArray, expectedOutput);
}

@Test
public void shellSortDuplicateStringArray() {
String[] inputArray = {"s", "b", "d", "a", "d", "c", "h", "b"};
String[] outputArray = shellSort.sort(inputArray);
String[] expectedOutput = {"a", "b", "b", "c", "d", "d", "h", "s"};
assertArrayEquals(outputArray, expectedOutput);
public class ShellSortTest extends SortingAlgorithmTest {
@Override
SortAlgorithm getSortAlgorithm() {
return new ShellSort();
}
}