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/* $Id$ */
/*
* 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
/* Enable it if you suspect binary heap doesn't work well */
#define BINARYHEAP_CHECK 0
#if BINARYHEAP_CHECK
#define CHECK_CONSISTY() this->CheckConsistency()
#else
#define CHECK_CONSISTY() ;
#endif
/**
* Binary Heap as C++ template.
*
* For information about Binary Heap algotithm,
* see: http://www.policyalmanac.org/games/binaryHeaps.htm
*
* Implementation specific notes:
*
* 1) It allocates space for item pointers (array). Items are allocated elsewhere.
*
* 2) T*[0] is never used. Total array size is max_items + 1, because we
* use indices 1..max_items instead of zero based C indexing.
*
* 3) Item of the binary heap should support these public members:
* - 'lower-than' operator '<' - used for comparing items before moving
*
*/
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 heap item pointers
public:
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:
/** Heapify (move gap) down */
FORCEINLINE uint HeapifyDown(uint gap, T *item)
{
assert(gap != 0);
uint child = gap * 2; // first child is at [parent * 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;
}
/** Heapify (move gap) up */
FORCEINLINE 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
/** verifies the heap consistency (added during first YAPF debug phase) */
FORCEINLINE void CheckConsistency()
{
for (uint child = 2; child <= this->items; child++) {
uint parent = child / 2;
assert(!(*this->data[child] < *this->data[parent]));
}
}
#endif
public:
/** Return the number of items stored in the priority queue.
* @return number of items in the queue */
FORCEINLINE uint Size() const { return this->items; }
/** Test if the priority queue is empty.
* @return true if empty */
FORCEINLINE bool IsEmpty() const { return this->items == 0; }
/** Test if the priority queue is full.
* @return true if full. */
FORCEINLINE bool IsFull() const { return this->items >= this->capacity; }
/** Find the smallest item in the priority queue.
* Return the smallest item, or throw assert if empty. */
FORCEINLINE T *Begin()
{
assert(!this->IsEmpty());
return this->data[1];
}
FORCEINLINE T *End()
{
return this->data[1 + this->items];
}
/** Insert new item into the priority queue, maintaining heap order.
* @return false if the queue is full. */
FORCEINLINE void Push(T *new_item)
{
if (this->IsFull()) {
this->capacity *= 2;
this->data = ReallocT<T*>(this->data, this->capacity + 1);
}
/* make place for new item */
uint gap = this->HeapifyUp(++items, new_item);
this->data[gap] = new_item;
CHECK_CONSISTY();
}
/** Remove and return the smallest item from the priority queue. */
FORCEINLINE 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 specified by index */
FORCEINLINE void RemoveByIdx(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();
}
/** return index of the item that matches (using &item1 == &item2) the given item. */
FORCEINLINE uint FindLinear(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. */
FORCEINLINE void Clear() { this->items = 0; }
};
#endif /* BINARYHEAP_HPP */
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