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3 | 3 | import java.util.Arrays; |
4 | 4 |
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5 | 5 | public class QuickSort { |
6 | | - |
| 6 | + |
7 | 7 | public void sort(int[] array) { |
8 | 8 | if (array.length < 2) { |
9 | 9 | return; |
10 | 10 | } |
11 | 11 |
|
12 | 12 | quickSort(array, 0, array.length - 1); |
| 13 | + System.out.println(swaps); |
13 | 14 | } |
14 | 15 |
|
15 | 16 | private void quickSort(int[] array, int min, int max) { |
16 | 17 | // Base case, partition is of size one or null |
17 | | - if (min >= max) { |
| 18 | + if (min > max) { |
18 | 19 | return; |
19 | 20 | } |
20 | 21 |
|
21 | | - // Set starting pivot at last position |
22 | | - int pivot = max; |
| 22 | + // Reorder partition so that x < pivot on the left and x >= pivot on the right |
| 23 | + // Returned int is the index of the pivot |
| 24 | + int pivot = partition(array, min, max); |
| 25 | + |
| 26 | + // Recursively apply quick sort to left and right side of list |
| 27 | + quickSort(array, min, pivot - 1); |
| 28 | + quickSort(array, pivot + 1, max); |
| 29 | + } |
| 30 | + |
| 31 | + private int partition(int[] array, int min, int max) { |
| 32 | + int pivot = array[max]; |
23 | 33 | int left = min; |
24 | 34 | int right = max; |
25 | 35 |
|
26 | 36 | // Repeat until pointers meet |
27 | | - while (left < right) { |
28 | | - // Continue until left side swap candidate is found |
29 | | - while (array[left] < array[pivot]) { |
| 37 | + while (true) { |
| 38 | + // Keep moving left pointer until swap candidate is found |
| 39 | + while (array[left] < pivot) { |
30 | 40 | left++; |
31 | 41 | } |
32 | | - |
33 | | - // Swap and update pivot index |
34 | | - swap(array, left, pivot); |
35 | | - pivot = left; |
36 | | - |
37 | | - // Continue until right side swap candidate is found |
38 | | - while (array[right] > array[pivot]) { |
| 42 | + // Same for right pointer |
| 43 | + while (array[right] > pivot) { |
39 | 44 | right--; |
40 | 45 | } |
41 | 46 |
|
42 | | - // Swap and update pivot index |
43 | | - swap(array, right, pivot); |
44 | | - pivot = right; |
| 47 | + // If pointers met, we're done on this partition, pivot is on right pointer |
| 48 | + if (left >= right) { |
| 49 | + return right; |
| 50 | + } |
| 51 | + |
| 52 | + // Swap elements |
| 53 | + swap(array, left, right); |
45 | 54 | } |
46 | | - |
47 | | - // Recursively apply quick sort to left and right side of list |
48 | | - quickSort(array, min, pivot - 1); |
49 | | - quickSort(array, pivot + 1, max); |
50 | 55 | } |
51 | | - |
52 | 56 |
|
53 | 57 | private void swap(int[] array, int a, int b) { |
54 | 58 | int temp = array[a]; |
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