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Location: cpp/openttd-patchpack/source/src/misc/binaryheap.hpp
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(svn r27534) -Fix [FS#6435]: [NewGRF] Station spritelayouts did not accept the var10 flag for the palette.
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/*
* This file is part of OpenTTD.
* OpenTTD 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, version 2.
* OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
*/
/** @file binaryheap.hpp Binary heap implementation. */
#ifndef BINARYHEAP_HPP
#define BINARYHEAP_HPP
#include "../core/alloc_func.hpp"
/** Enable it if you suspect binary heap doesn't work well */
#define BINARYHEAP_CHECK 0
#if BINARYHEAP_CHECK
/** Check for consistency. */
#define CHECK_CONSISTY() this->CheckConsistency()
#else
/** Don't check for consistency. */
#define CHECK_CONSISTY() ;
#endif
/**
* Binary Heap as C++ template.
* A carrier which keeps its items automatically holds the smallest item at
* the first position. The order of items is maintained by using a binary tree.
* The implementation is used for priority queue's.
*
* @par Usage information:
* Item of the binary heap should support the 'lower-than' operator '<'.
* It is used for comparing items before moving them to their position.
*
* @par
* This binary heap allocates just the space for item pointers. The items
* are allocated elsewhere.
*
* @par Implementation notes:
* Internally the first item is never used, because that simplifies the
* implementation.
*
* @par
* For further information about the Binary Heap algorithm, see
* http://www.policyalmanac.org/games/binaryHeaps.htm
*
* @tparam T Type of the items stored in the binary heap
*/
template <class T>
class CBinaryHeapT {
private:
uint items; ///< Number of items in the heap
uint capacity; ///< Maximum number of items the heap can hold
T **data; ///< The pointer to the heap item pointers
public:
/**
* Create a binary heap.
* @param max_items The limit of the heap
*/
explicit CBinaryHeapT(uint max_items)
: items(0)
, capacity(max_items)
{
this->data = MallocT<T *>(max_items + 1);
}
~CBinaryHeapT()
{
this->Clear();
free(this->data);
this->data = NULL;
}
protected:
/**
* Get position for fixing a gap (downwards).
* The gap is moved downwards in the binary tree until it
* is in order again.
*
* @param gap The position of the gap
* @param item The proposed item for filling the gap
* @return The (gap)position where the item fits
*/
inline uint HeapifyDown(uint gap, T *item)
{
assert(gap != 0);
/* The first child of the gap is at [parent * 2] */
uint child = gap * 2;
/* while children are valid */
while (child <= this->items) {
/* choose the smaller child */
if (child < this->items && *this->data[child + 1] < *this->data[child]) {
child++;
}
/* is it smaller than our parent? */
if (!(*this->data[child] < *item)) {
/* the smaller child is still bigger or same as parent => we are done */
break;
}
/* if smaller child is smaller than parent, it will become new parent */
this->data[gap] = this->data[child];
gap = child;
/* where do we have our new children? */
child = gap * 2;
}
return gap;
}
/**
* Get position for fixing a gap (upwards).
* The gap is moved upwards in the binary tree until the
* is in order again.
*
* @param gap The position of the gap
* @param item The proposed item for filling the gap
* @return The (gap)position where the item fits
*/
inline uint HeapifyUp(uint gap, T *item)
{
assert(gap != 0);
uint parent;
while (gap > 1) {
/* compare [gap] with its parent */
parent = gap / 2;
if (!(*item < *this->data[parent])) {
/* we don't need to continue upstairs */
break;
}
this->data[gap] = this->data[parent];
gap = parent;
}
return gap;
}
#if BINARYHEAP_CHECK
/** Verify the heap consistency */
inline void CheckConsistency()
{
for (uint child = 2; child <= this->items; child++) {
uint parent = child / 2;
assert(!(*this->data[child] < *this->data[parent]));
}
}
#endif
public:
/**
* Get the number of items stored in the priority queue.
*
* @return The number of items in the queue
*/
inline uint Length() const
{
return this->items;
}
/**
* Test if the priority queue is empty.
*
* @return True if empty
*/
inline bool IsEmpty() const
{
return this->items == 0;
}
/**
* Test if the priority queue is full.
*
* @return True if full.
*/
inline bool IsFull() const
{
return this->items >= this->capacity;
}
/**
* Get the smallest item in the binary tree.
*
* @return The smallest item, or throw assert if empty.
*/
inline T *Begin()
{
assert(!this->IsEmpty());
return this->data[1];
}
/**
* Get the LAST item in the binary tree.
*
* @note The last item is not necessary the biggest!
*
* @return The last item
*/
inline T *End()
{
return this->data[1 + this->items];
}
/**
* Insert new item into the priority queue, maintaining heap order.
*
* @param new_item The pointer to the new item
*/
inline void Include(T *new_item)
{
if (this->IsFull()) {
assert(this->capacity < UINT_MAX / 2);
this->capacity *= 2;
this->data = ReallocT<T*>(this->data, this->capacity + 1);
}
/* Make place for new item. A gap is now at the end of the tree. */
uint gap = this->HeapifyUp(++items, new_item);
this->data[gap] = new_item;
CHECK_CONSISTY();
}
/**
* Remove and return the smallest (and also first) item
* from the priority queue.
*
* @return The pointer to the removed item
*/
inline T *Shift()
{
assert(!this->IsEmpty());
T *first = this->Begin();
this->items--;
/* at index 1 we have a gap now */
T *last = this->End();
uint gap = this->HeapifyDown(1, last);
/* move last item to the proper place */
if (!this->IsEmpty()) this->data[gap] = last;
CHECK_CONSISTY();
return first;
}
/**
* Remove item at given index from the priority queue.
*
* @param index The position of the item in the heap
*/
inline void Remove(uint index)
{
if (index < this->items) {
assert(index != 0);
this->items--;
/* at position index we have a gap now */
T *last = this->End();
/* Fix binary tree up and downwards */
uint gap = this->HeapifyUp(index, last);
gap = this->HeapifyDown(gap, last);
/* move last item to the proper place */
if (!this->IsEmpty()) this->data[gap] = last;
} else {
assert(index == this->items);
this->items--;
}
CHECK_CONSISTY();
}
/**
* Search for an item in the priority queue.
* Matching is done by comparing address of the
* item.
*
* @param item The reference to the item
* @return The index of the item or zero if not found
*/
inline uint FindIndex(const T &item) const
{
if (this->IsEmpty()) return 0;
for (T **ppI = this->data + 1, **ppLast = ppI + this->items; ppI <= ppLast; ppI++) {
if (*ppI == &item) {
return ppI - this->data;
}
}
return 0;
}
/**
* Make the priority queue empty.
* All remaining items will remain untouched.
*/
inline void Clear()
{
this->items = 0;
}
};
#endif /* BINARYHEAP_HPP */
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