Java MergeSort
Java MergeSort
/** * <html> * <body> * <P> Copyright 1994-2018 JasonInternational </p> * <p> All rights reserved.</p> * <p> Created on 2018年4月10日 </p> * <p> Created by Jason</p> * </body> * </html> */ package cn.ucaner.algorithm.sorts; /** * Merge sort is an O(n log n) comparison-based sorting algorithm. Most * implementations produce a stable sort, which means that the implementation * preserves the input order of equal elements in the sorted output. * <p> * Family: Merging.<br> * Space: In-place.<br> * Stable: True.<br> * <p> * Average case = O(n*log n)<br> * Worst case = O(n*log n)<br> * Best case = O(n*log n)<br> * <p> * @see <a href="https://en.wikipedia.org/wiki/Merge_sort">Merge Sort (Wikipedia)</a> * <br> * @author Justin Wetherell <phishman3579@gmail.com> */ @SuppressWarnings("unchecked") public class MergeSort<T extends Comparable<T>> { public static enum SPACE_TYPE { IN_PLACE, NOT_IN_PLACE } private MergeSort() { } public static <T extends Comparable<T>> T[] sort(SPACE_TYPE type, T[] unsorted) { sort(type, 0, unsorted.length, unsorted); return unsorted; } private static <T extends Comparable<T>> void sort(SPACE_TYPE type, int start, int length, T[] unsorted) { if (length > 2) { int aLength = (int) Math.floor(length / 2); int bLength = length - aLength; sort(type, start, aLength, unsorted); sort(type, start + aLength, bLength, unsorted); if (type == SPACE_TYPE.IN_PLACE) mergeInPlace(start, aLength, start + aLength, bLength, unsorted); else mergeWithExtraStorage(start, aLength, start + aLength, bLength, unsorted); } else if (length == 2) { T e = unsorted[start + 1]; if (e.compareTo(unsorted[start]) < 0) { unsorted[start + 1] = unsorted[start]; unsorted[start] = e; } } } private static <T extends Comparable<T>> void mergeInPlace(int aStart, int aLength, int bStart, int bLength, T[] unsorted) { int i = aStart; int j = bStart; int aSize = aStart + aLength; int bSize = bStart + bLength; while (i < aSize && j < bSize) { T a = unsorted[i]; T b = unsorted[j]; if (b.compareTo(a) < 0) { // Shift everything to the right one spot System.arraycopy(unsorted, i, unsorted, i+1, j-i); unsorted[i] = b; i++; j++; aSize++; } else { i++; } } } private static <T extends Comparable<T>> void mergeWithExtraStorage(int aStart, int aLength, int bStart, int bLength, T[] unsorted) { int count = 0; T[] output = (T[]) new Comparable[aLength + bLength]; int i = aStart; int j = bStart; int aSize = aStart + aLength; int bSize = bStart + bLength; while (i < aSize || j < bSize) { T a = null; if (i < aSize) { a = unsorted[i]; } T b = null; if (j < bSize) { b = unsorted[j]; } if (a != null && b == null) { output[count++] = a; i++; } else if (b != null && a == null) { output[count++] = b; j++; } else if (b != null && b.compareTo(a) <= 0) { output[count++] = b; j++; } else { output[count++] = a; i++; } } int x = 0; int size = aStart + aLength + bLength; for (int y = aStart; y < size; y++) { unsorted[y] = output[x++]; } } }
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