/*
* Copyright (c) 2020 Red Hat, Inc.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* $Id: //eng/vdo-releases/aluminum/src/c++/vdo/base/heap.h#2 $
*/
#ifndef HEAP_H
#define HEAP_H
#include "common.h"
/**
* Prototype for functions which compare two array elements. All the time
* complexity claims in this module assume this operation has O(1) time
* complexity.
*
* @param item1 The first element to compare
* @param item2 The second element to compare
*
* @return An integer which is less than, equal to, or greater than 0
* depending on whether item1 is less than, equal to, or greater
* than item2, respectively
**/
typedef int HeapComparator(const void *item1, const void *item2);
/**
* Prototype for functions which swap two array elements.
*
* @param item1 The first element to swap
* @param item2 The second element to swap
**/
typedef void HeapSwapper(void *item1, void *item2);
/**
* A heap array can be any array of fixed-length elements in which the heap
* invariant can be established. In a max-heap, every child of a node must be
* at least as large as its children. Once that invariant is established in an
* array by calling buildHeap(), all the other heap operations may be used on
* that array.
**/
typedef struct heap {
/** the 1-based array of heap elements (nodes) */
byte *array;
/** the function to use to compare two elements */
HeapComparator *comparator;
/** the function to use to swap two elements */
HeapSwapper *swapper;
/** the maximum number of elements that can be stored */
size_t capacity;
/** the size of every element (in bytes) */
size_t elementSize;
/** the current number of elements in the heap */
size_t count;
} Heap;
/**
* Initialize an binary heap by wrapping it around an array of elements.
*
* The heap will not own the array it wraps. Use buildHeap() subsequently to
* arrange any elements contained in the array into a valid heap.
*
* @param heap The heap to initialize
* @param comparator The function to use to compare two heap elements
* @param swapper The function to use to swap two heap elements
* @param array The array of elements (not modified by this call)
* @param capacity The maximum number of elements which fit in the array
* @param elementSize The size of every array element, in bytes
**/
void initializeHeap(Heap *heap,
HeapComparator *comparator,
HeapSwapper *swapper,
void *array,
size_t capacity,
size_t elementSize);
/**
* Build a max-heap in place in an array (heapify it) by re-ordering the
* elements to establish the heap invariant. Before calling this function,
* first copy the elements to be arranged into a heap into the array that was
* passed to initializeHeap(). This operation has O(N) time complexity in the
* number of elements in the array.
*
* @param heap The heap to build
* @param count The number of elements in the array to build into a heap
**/
void buildHeap(Heap *heap, size_t count);
/**
* Check whether the heap is currently empty.
*
* @param heap The heap to query
*
* @return <code>true</code> if there are no elements in the heap
**/
static inline bool isHeapEmpty(const Heap *heap)
{
return (heap->count == 0);
}
/**
* Remove the largest element from the top of the heap and restore the heap
* invariant on the remaining elements. This operation has O(log2(N)) time
* complexity.
*
* @param [in] heap The heap to modify
* @param [out] elementPtr A pointer to receive the largest element (may be
* NULL if the caller just wishes to discard it)
*
* @return <code>false</code> if the heap was empty, so no element was removed
**/
bool popMaxHeapElement(Heap *heap, void *elementPtr);
/**
* Sort the elements contained in a heap.
*
* This function re-orders the elements contained in the heap to a sorted
* array in-place by repeatedly popping the maximum element off the heap and
* moving it to the spot vacated at the end of the heap array. When the
* function returns, the heap will be empty and the array will contain the
* elements in sorted order, from heap minimum to heap maximum. The sort is
* unstable--relative ordering of equal keys is not preserved. This operation
* has O(N*log2(N)) time complexity.
*
* @param heap The heap containing the elements to sort
*
* @return the number of elements that were sorted
**/
size_t sortHeap(Heap *heap);
/**
* Gets the next sorted heap element and returns a pointer to it, in O(log2(N))
* time.
*
* @param heap The heap to sort one more step
*
* @return a pointer to the element sorted, or NULL if already fully sorted.
**/
void *sortNextHeapElement(Heap *heap);
#endif /* HEAP_H */