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/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / Utils / FixedMaxHeap.cs / 1305376 / FixedMaxHeap.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== // =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ // // FixedMaxHeap.cs // //[....] // // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- using System.Collections.Generic; using System.Diagnostics.Contracts; namespace System.Linq.Parallel { ////// Very simple heap data structure, of fixed size. /// ///internal class FixedMaxHeap { private TElement[] m_elements; // Element array. private int m_count; // Current count. private IComparer m_comparer; // Element comparison routine. //------------------------------------------------------------------------------------ // Create a new heap with the specified maximum size. // internal FixedMaxHeap(int maximumSize) : this(maximumSize, Util.GetDefaultComparer ()) { } internal FixedMaxHeap(int maximumSize, IComparer comparer) { m_elements = new TElement[maximumSize]; m_comparer = comparer; } //----------------------------------------------------------------------------------- // Retrieve the count (i.e. how many elements are in the heap). // internal int Count { get { return m_count; } } //----------------------------------------------------------------------------------- // Retrieve the size (i.e. the maximum size of the heap). // internal int Size { get { return m_elements.Length; } } //----------------------------------------------------------------------------------- // Get the current maximum value in the max-heap. // // Note: The heap stores the maximumSize smallest elements that were inserted. // So, if the heap is full, the value returned is the maximumSize-th smallest // element that was inserted into the heap. // internal TElement MaxValue { get { if (m_count == 0) { throw new InvalidOperationException(SR.GetString(SR.NoElements)); } // The maximum element is in the 0th position. return m_elements[0]; } } //------------------------------------------------------------------------------------ // Removes all elements from the heap. // internal void Clear() { m_count = 0; } //----------------------------------------------------------------------------------- // Inserts the new element, maintaining the heap property. // // Return Value: // If the element is greater than the current max element, this function returns // false without modifying the heap. Otherwise, it returns true. // internal bool Insert(TElement e) { if (m_count < m_elements.Length) { // There is room. We can add it and then max-heapify. m_elements[m_count] = e; m_count++; HeapifyLastLeaf(); return true; } else { // No more room. The element might not even fit in the heap. The check // is simple: if it's greater than the maximum element, then it can't be // inserted. Otherwise, we replace the head with it and reheapify. if (m_comparer.Compare(e, m_elements[0]) < 0) { m_elements[0] = e; HeapifyRoot(); return true; } return false; } } //------------------------------------------------------------------------------------ // Replaces the maximum value in the heap with the user-provided value, and restores // the heap property. // internal void ReplaceMax(TElement newValue) { Contract.Assert(m_count > 0); m_elements[0] = newValue; HeapifyRoot(); } //------------------------------------------------------------------------------------ // Removes the maximum value from the heap, and restores the heap property. // internal void RemoveMax() { Contract.Assert(m_count > 0); m_count--; if (m_count > 0) { m_elements[0] = m_elements[m_count]; HeapifyRoot(); } } //----------------------------------------------------------------------------------- // Private helpers to swap elements, and to reheapify starting from the root or // from a leaf element, depending on what is needed. // private void Swap(int i, int j) { TElement tmpElement = m_elements[i]; m_elements[i] = m_elements[j]; m_elements[j] = tmpElement; } private void HeapifyRoot() { // We are heapifying from the head of the list. int i = 0; int n = m_count; while (i < n) { // Calculate the current child node indexes. int n0 = ((i + 1) * 2) - 1; int n1 = n0 + 1; if (n0 < n && m_comparer.Compare(m_elements[i], m_elements[n0]) < 0) { // We have to select the bigger of the two subtrees, and float // the current element down. This maintains the max-heap property. if (n1 < n && m_comparer.Compare(m_elements[n0], m_elements[n1]) < 0) { Swap(i, n1); i = n1; } else { Swap(i, n0); i = n0; } } else if (n1 < n && m_comparer.Compare(m_elements[i], m_elements[n1]) < 0) { // Float down the "right" subtree. We needn't compare this subtree // to the "left", because if the element was smaller than that, the // first if statement's predicate would have evaluated to true. Swap(i, n1); i = n1; } else { // Else, the current key is in its final position. Break out // of the current loop and return. break; } } } private void HeapifyLastLeaf() { int i = m_count - 1; while (i > 0) { int j = ((i + 1) / 2) - 1; if (m_comparer.Compare(m_elements[i], m_elements[j]) > 0) { Swap(i, j); i = j; } else { break; } } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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