67 lines
1.5 KiB
C#
67 lines
1.5 KiB
C#
//
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// Author:
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// Jb Evain (jbevain@gmail.com)
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//
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// Copyright (c) 2008 - 2015 Jb Evain
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// Copyright (c) 2008 - 2011 Novell, Inc.
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//
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// Licensed under the MIT/X11 license.
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//
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using System;
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using System.Collections.Generic;
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namespace MonoFN {
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class MergeSort<T> {
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private readonly T [] elements;
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private readonly T [] buffer;
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private readonly IComparer<T> comparer;
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private MergeSort (T [] elements, IComparer<T> comparer)
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{
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this.elements = elements;
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this.buffer = new T [elements.Length];
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Array.Copy (this.elements, this.buffer, elements.Length);
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this.comparer = comparer;
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}
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public static void Sort (T [] source, IComparer<T> comparer)
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{
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Sort (source, 0, source.Length, comparer);
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}
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public static void Sort (T [] source, int start, int length, IComparer<T> comparer)
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{
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new MergeSort<T> (source, comparer).Sort (start, length);
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}
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private void Sort (int start, int length)
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{
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TopDownSplitMerge (this.buffer, this.elements, start, length);
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}
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private void TopDownSplitMerge (T [] a, T [] b, int start, int end)
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{
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if (end - start < 2)
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return;
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int middle = (end + start) / 2;
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TopDownSplitMerge (b, a, start, middle);
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TopDownSplitMerge (b, a, middle, end);
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TopDownMerge (a, b, start, middle, end);
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}
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private void TopDownMerge (T [] a, T [] b, int start, int middle, int end)
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{
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for (int i = start, j = middle, k = start; k < end; k++) {
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if (i < middle && (j >= end || comparer.Compare (a [i], a [j]) <= 0)) {
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b [k] = a [i++];
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} else {
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b [k] = a [j++];
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}
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}
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}
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}
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}
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