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4 | 4 | import java.util.function.BiPredicate; |
5 | 5 |
|
6 | 6 | /** |
7 | | - * BitonicSort class implements the SortAlgorithm interface using the bitonic sort technique. |
| 7 | + * BitonicSort class implements the SortAlgorithm interface using the bitonic |
| 8 | + * sort technique. |
8 | 9 | */ |
9 | 10 | public class BitonicSort implements SortAlgorithm { |
10 | | - private enum Direction { |
11 | | - DESCENDING, |
12 | | - ASCENDING, |
13 | | - } |
14 | | - |
15 | | - /** |
16 | | - * Sorts the given array using the Bitonic Sort algorithm. |
17 | | - * |
18 | | - * @param <T> the type of elements in the array, which must implement the Comparable interface |
19 | | - * @param array the array to be sorted |
20 | | - * @return the sorted array |
21 | | - */ |
22 | | - @Override |
23 | | - public <T extends Comparable<T>> T[] sort(T[] array) { |
24 | | - if (array.length == 0) { |
25 | | - return array; |
26 | | - } |
27 | | - |
28 | | - final int paddedSize = nextPowerOfTwo(array.length); |
29 | | - T[] paddedArray = Arrays.copyOf(array, paddedSize); |
30 | | - |
31 | | - // Fill the padded part with a maximum value |
32 | | - final T maxValue = max(array); |
33 | | - Arrays.fill(paddedArray, array.length, paddedSize, maxValue); |
34 | | - |
35 | | - bitonicSort(paddedArray, 0, paddedSize, Direction.ASCENDING); |
36 | | - return Arrays.copyOf(paddedArray, array.length); |
37 | | - } |
38 | | - |
39 | | - private <T extends Comparable<T>> void bitonicSort(final T[] array, final int low, final int cnt, final Direction direction) { |
40 | | - if (cnt > 1) { |
41 | | - final int k = cnt / 2; |
42 | | - |
43 | | - // Sort first half in ascending order |
44 | | - bitonicSort(array, low, k, Direction.ASCENDING); |
45 | | - |
46 | | - // Sort second half in descending order |
47 | | - bitonicSort(array, low + k, cnt - k, Direction.DESCENDING); |
48 | | - |
49 | | - // Merge the whole sequence in ascending order |
50 | | - bitonicMerge(array, low, cnt, direction); |
51 | | - } |
52 | | - } |
53 | | - |
54 | | - /** |
55 | | - * Merges the bitonic sequence in the specified direction. |
56 | | - * |
57 | | - * @param <T> the type of elements in the array, which must be Comparable |
58 | | - * @param array the array containing the bitonic sequence to be merged |
59 | | - * @param low the starting index of the sequence to be merged |
60 | | - * @param cnt the number of elements in the sequence to be merged |
61 | | - * @param direction the direction of sorting |
62 | | - */ |
63 | | - private <T extends Comparable<T>> void bitonicMerge(T[] array, int low, int cnt, Direction direction) { |
64 | | - if (cnt > 1) { |
65 | | - final int k = cnt / 2; |
66 | | - |
67 | | - final BiPredicate<T, T> areSorted = (direction == Direction.ASCENDING) ? (a, b) -> SortUtils.less(a,b) : (a, b) -> SortUtils.greater(a,b); |
68 | | - for (int i = low; i < low + k; i++) { |
69 | | - if (!areSorted.test(array[i], array[i + k])) { |
70 | | - SortUtils.swap(array, i, i + k); |
71 | | - } |
72 | | - } |
73 | | - |
74 | | - bitonicMerge(array, low, k, direction); |
75 | | - bitonicMerge(array, low + k, cnt - k, direction); |
76 | | - } |
77 | | - } |
78 | | - |
79 | | - /** |
80 | | - * Finds the next power of two greater than or equal to the given number. |
81 | | - * |
82 | | - * @param n the number |
83 | | - * @return the next power of two |
84 | | - */ |
85 | | - private static int nextPowerOfTwo(int n) { |
86 | | - int count = 0; |
87 | | - |
88 | | - // First n in the below condition is for the case where n is 0 |
89 | | - if ((n & (n - 1)) == 0) { |
90 | | - return n; |
91 | | - } |
92 | | - |
93 | | - while (n != 0) { |
94 | | - n >>= 1; |
95 | | - count += 1; |
96 | | - } |
97 | | - |
98 | | - return 1 << count; |
99 | | - } |
100 | | - |
101 | | - /** |
102 | | - * Finds the maximum element in the given array. |
103 | | - * |
104 | | - * @param <T> the type of elements in the array, which must implement the Comparable interface |
105 | | - * @param array the array to be searched |
106 | | - * @return the maximum element in the array |
107 | | - * @throws IllegalArgumentException if the array is null or empty |
108 | | - */ |
109 | | - private static <T extends Comparable<T>> T max(final T[] array) { |
110 | | - return Arrays.stream(array).max(Comparable::compareTo).orElseThrow(); |
111 | | - } |
| 11 | + private enum Direction { |
| 12 | + DESCENDING, ASCENDING, |
| 13 | + } |
| 14 | + |
| 15 | + /** |
| 16 | + * Sorts the given array using the Bitonic Sort algorithm. |
| 17 | + * |
| 18 | + * @param <T> the type of elements in the array, which must implement the |
| 19 | + * Comparable interface |
| 20 | + * @param array the array to be sorted |
| 21 | + * @return the sorted array |
| 22 | + */ |
| 23 | + @Override |
| 24 | + public <T extends Comparable<T>> T[] sort(T[] array) { |
| 25 | + if (array.length == 0) { |
| 26 | + return array; |
| 27 | + } |
| 28 | + |
| 29 | + final int paddedSize = nextPowerOfTwo(array.length); |
| 30 | + T[] paddedArray = Arrays.copyOf(array, paddedSize); |
| 31 | + |
| 32 | + // Fill the padded part with a maximum value |
| 33 | + final T maxValue = max(array); |
| 34 | + Arrays.fill(paddedArray, array.length, paddedSize, maxValue); |
| 35 | + |
| 36 | + bitonicSort(paddedArray, 0, paddedSize, Direction.ASCENDING); |
| 37 | + return Arrays.copyOf(paddedArray, array.length); |
| 38 | + } |
| 39 | + |
| 40 | + private <T extends Comparable<T>> void bitonicSort(final T[] array, final int low, final int cnt, |
| 41 | + final Direction direction) { |
| 42 | + if (cnt > 1) { |
| 43 | + final int k = cnt / 2; |
| 44 | + |
| 45 | + // Sort first half in ascending order |
| 46 | + bitonicSort(array, low, k, Direction.ASCENDING); |
| 47 | + |
| 48 | + // Sort second half in descending order |
| 49 | + bitonicSort(array, low + k, cnt - k, Direction.DESCENDING); |
| 50 | + |
| 51 | + // Merge the whole sequence in ascending order |
| 52 | + bitonicMerge(array, low, cnt, direction); |
| 53 | + } |
| 54 | + } |
| 55 | + |
| 56 | + /** |
| 57 | + * Merges the bitonic sequence in the specified direction. |
| 58 | + * |
| 59 | + * @param <T> the type of elements in the array, which must be Comparable |
| 60 | + * @param array the array containing the bitonic sequence to be merged |
| 61 | + * @param low the starting index of the sequence to be merged |
| 62 | + * @param cnt the number of elements in the sequence to be merged |
| 63 | + * @param direction the direction of sorting |
| 64 | + */ |
| 65 | + private <T extends Comparable<T>> void bitonicMerge(T[] array, int low, int cnt, Direction direction) { |
| 66 | + if (cnt > 1) { |
| 67 | + final int k = cnt / 2; |
| 68 | + |
| 69 | + final BiPredicate<T, T> areSorted = (direction == Direction.ASCENDING) ? (a, b) -> SortUtils.less(a, b) |
| 70 | + : (a, b) -> SortUtils.greater(a, b); |
| 71 | + for (int i = low; i < low + k; i++) { |
| 72 | + if (!areSorted.test(array[i], array[i + k])) { |
| 73 | + SortUtils.swap(array, i, i + k); |
| 74 | + } |
| 75 | + } |
| 76 | + |
| 77 | + bitonicMerge(array, low, k, direction); |
| 78 | + bitonicMerge(array, low + k, cnt - k, direction); |
| 79 | + } |
| 80 | + } |
| 81 | + |
| 82 | + /** |
| 83 | + * Finds the next power of two greater than or equal to the given number. |
| 84 | + * |
| 85 | + * @param n the number |
| 86 | + * @return the next power of two |
| 87 | + */ |
| 88 | + private static int nextPowerOfTwo(int n) { |
| 89 | + int count = 0; |
| 90 | + |
| 91 | + // First n in the below condition is for the case where n is 0 |
| 92 | + if ((n & (n - 1)) == 0) { |
| 93 | + return n; |
| 94 | + } |
| 95 | + |
| 96 | + while (n != 0) { |
| 97 | + n >>= 1; |
| 98 | + count += 1; |
| 99 | + } |
| 100 | + |
| 101 | + return 1 << count; |
| 102 | + } |
| 103 | + |
| 104 | + /** |
| 105 | + * Finds the maximum element in the given array. |
| 106 | + * |
| 107 | + * @param <T> the type of elements in the array, which must implement the |
| 108 | + * Comparable interface |
| 109 | + * @param array the array to be searched |
| 110 | + * @return the maximum element in the array |
| 111 | + * @throws IllegalArgumentException if the array is null or empty |
| 112 | + */ |
| 113 | + private static <T extends Comparable<T>> T max(final T[] array) { |
| 114 | + return Arrays.stream(array).max(Comparable::compareTo).orElseThrow(); |
| 115 | + } |
112 | 116 | } |
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