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| 1 | +package ch_23; |
| 2 | + |
| 3 | +import java.util.Arrays; |
| 4 | +import java.util.Comparator; |
| 5 | + |
| 6 | +/** |
| 7 | + * 23.3 (Generic quick sort) Write the following two generic methods using quick sort. |
| 8 | + * The first method sorts the elements using the Comparable interface and the |
| 9 | + * second uses the Comparator interface. |
| 10 | + * public static <E extends Comparable<E>> |
| 11 | + * void quickSort(E[] list) |
| 12 | + * public static <E> void quickSort(E[] list, |
| 13 | + * Comparator<? super E> comparator) |
| 14 | + */ |
| 15 | +public class Exercise23_03 { |
| 16 | + |
| 17 | + public static void main(String[] args) { |
| 18 | + Integer[] arr = new Integer[]{23, 25, 7, 14, 85, 65}; |
| 19 | + quickSort(arr); |
| 20 | + System.out.println(Arrays.toString(arr)); |
| 21 | + |
| 22 | + Integer[] arr2 = new Integer[]{3, 2, 7, 4, 8, 6, 1, 7}; |
| 23 | + quickSort(arr2, Integer::compareTo); |
| 24 | + System.out.println(Arrays.toString(arr2)); |
| 25 | + |
| 26 | + } |
| 27 | + |
| 28 | + // Using Comparable |
| 29 | + public static <E extends Comparable<E>> void quickSort(E[] list) { |
| 30 | + quickSort(list, 0, list.length - 1); |
| 31 | + } |
| 32 | + |
| 33 | + public static <E extends Comparable<E>> void quickSort(E[] list, int first, int last) { |
| 34 | + if (last > first) { |
| 35 | + int pivotIndex = partition(list, first, last); |
| 36 | + quickSort(list, first, pivotIndex - 1); |
| 37 | + quickSort(list, pivotIndex + 1, last); |
| 38 | + } |
| 39 | + } |
| 40 | + |
| 41 | + public static <E extends Comparable<E>> int partition(E[] list, int first, int last) { |
| 42 | + E pivot = list[first]; // Choose the first element as the pivot |
| 43 | + int low = first + 1; // Index for forward search |
| 44 | + int high = last; // Index for backward search |
| 45 | + |
| 46 | + while (high > low) { |
| 47 | + // Search forward from left |
| 48 | + while (low <= high && list[low].compareTo(pivot) <= 0) low++; |
| 49 | + |
| 50 | + // Search backward from right |
| 51 | + while (low <= high && list[high].compareTo(pivot) > 0) high--; |
| 52 | + |
| 53 | + // Swap two elements in the list |
| 54 | + if (high > low) { |
| 55 | + E temp = list[high]; |
| 56 | + list[high] = list[low]; |
| 57 | + list[low] = temp; |
| 58 | + } |
| 59 | + } |
| 60 | + |
| 61 | + while (high > first && list[high].compareTo(pivot) >= 0) |
| 62 | + high--; |
| 63 | + |
| 64 | + // Swap pivot with list[high] |
| 65 | + if (pivot.compareTo(list[high]) > 0) { |
| 66 | + list[first] = list[high]; |
| 67 | + list[high] = pivot; |
| 68 | + return high; |
| 69 | + } else { |
| 70 | + return first; |
| 71 | + } |
| 72 | + } |
| 73 | + |
| 74 | + // Using Comparator |
| 75 | + public static <E> void quickSort(E[] list, |
| 76 | + Comparator<? super E> comparator) { |
| 77 | + quickSort(list, 0, list.length - 1, comparator); |
| 78 | + |
| 79 | + |
| 80 | + } |
| 81 | + |
| 82 | + // Using Comparator |
| 83 | + public static <E> void quickSort(E[] list, int first, int last, |
| 84 | + Comparator<? super E> comparator) { |
| 85 | + if (last > first) { |
| 86 | + int pivotIndex; |
| 87 | + // find pivot index |
| 88 | + E pivot = list[first]; // Choose the first element as the pivot |
| 89 | + int low = first + 1; // Index for forward search |
| 90 | + int high = last; // Index for backward search |
| 91 | + |
| 92 | + while (high > low) { |
| 93 | + // Search forward from left |
| 94 | + while (low <= high && comparator.compare(list[low], pivot) <= 0) low++; |
| 95 | + |
| 96 | + // Search backward from right |
| 97 | + while (low <= high && comparator.compare(list[high], pivot) > 0) high--; |
| 98 | + |
| 99 | + // Swap two elements in the list |
| 100 | + if (high > low) { |
| 101 | + E temp = list[high]; |
| 102 | + list[high] = list[low]; |
| 103 | + list[low] = temp; |
| 104 | + } |
| 105 | + } |
| 106 | + |
| 107 | + while (high > first && comparator.compare(list[high], pivot) >= 0) |
| 108 | + high--; |
| 109 | + |
| 110 | + // Swap pivot with list[high] |
| 111 | + if (comparator.compare(pivot, list[high]) > 0) { |
| 112 | + list[first] = list[high]; |
| 113 | + list[high] = pivot; |
| 114 | + pivotIndex = high; |
| 115 | + } else { |
| 116 | + pivotIndex = first; |
| 117 | + } |
| 118 | + |
| 119 | + quickSort(list, first, pivotIndex - 1, comparator); |
| 120 | + quickSort(list, pivotIndex + 1, last, comparator); |
| 121 | + } |
| 122 | + } |
| 123 | + |
| 124 | +} |
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