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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
/**
* 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) ItemPtr [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 Titem_>
class CBinaryHeapT {
public:
typedef Titem_ *ItemPtr;
private:
int m_size; ///< Number of items in the heap
int m_max_size; ///< Maximum number of items the heap can hold
ItemPtr *m_items; ///< The heap item pointers
public:
explicit CBinaryHeapT(int max_items)
: m_size(0)
, m_max_size(max_items)
{
m_items = MallocT<ItemPtr>(max_items + 1);
}
~CBinaryHeapT()
{
Clear();
free(m_items);
m_items = NULL;
}
public:
/** Return the number of items stored in the priority queue.
* @return number of items in the queue */
FORCEINLINE int Size() const {return m_size;};
/** Test if the priority queue is empty.
* @return true if empty */
FORCEINLINE bool IsEmpty() const {return (m_size == 0);};
/** Test if the priority queue is full.
* @return true if full. */
FORCEINLINE bool IsFull() const {return (m_size >= m_max_size);};
/** Find the smallest item in the priority queue.
* Return the smallest item, or throw assert if empty. */
FORCEINLINE Titem_& GetHead() {assert(!IsEmpty()); return *m_items[1];}
/** Insert new item into the priority queue, maintaining heap order. */
void Push(Titem_& new_item);
/** Remove and return the smallest item from the priority queue. */
FORCEINLINE Titem_& PopHead() {Titem_& ret = GetHead(); RemoveHead(); return ret;};
/** Remove the smallest item from the priority queue. */
void RemoveHead();
/** Remove item specified by index */
void RemoveByIdx(int idx);
/** return index of the item that matches (using &item1 == &item2) the given item. */
int FindLinear(const Titem_& item) const;
/** Make the priority queue empty.
* All remaining items will remain untouched. */
void Clear() {m_size = 0;};
/** verifies the heap consistency (added during first YAPF debug phase) */
void CheckConsistency();
};
template <class Titem_>
FORCEINLINE void CBinaryHeapT<Titem_>::Push(Titem_& new_item)
{
if (IsFull()) {
m_max_size *= 2;
m_items = ReallocT<ItemPtr>(m_items, m_max_size + 1);
}
/* make place for new item */
int gap = ++m_size;
/* Heapify up */
for (int parent = gap / 2; (parent > 0) && (new_item < *m_items[parent]); gap = parent, parent /= 2)
m_items[gap] = m_items[parent];
m_items[gap] = &new_item;
CheckConsistency();
}
template <class Titem_>
FORCEINLINE void CBinaryHeapT<Titem_>::RemoveHead()
{
assert(!IsEmpty());
/* at index 1 we have a gap now */
int gap = 1;
/* Heapify down:
* last item becomes a candidate for the head. Call it new_item. */
Titem_& new_item = *m_items[m_size--];
/* now we must maintain relation between parent and its children:
* parent <= any child
* from head down to the tail */
int child = 2; // first child is at [parent * 2]
/* while children are valid */
while (child <= m_size) {
/* choose the smaller child */
if (child < m_size && *m_items[child + 1] < *m_items[child])
child++;
/* is it smaller than our parent? */
if (!(*m_items[child] < new_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 */
m_items[gap] = m_items[child];
gap = child;
/* where do we have our new children? */
child = gap * 2;
}
/* move last item to the proper place */
if (m_size > 0) m_items[gap] = &new_item;
CheckConsistency();
}
template <class Titem_>
inline void CBinaryHeapT<Titem_>::RemoveByIdx(int idx)
{
/* at position idx we have a gap now */
int gap = idx;
Titem_& last = *m_items[m_size];
if (idx < m_size) {
assert(idx >= 1);
m_size--;
/* and the candidate item for fixing this gap is our last item 'last'
* Move gap / last item up: */
while (gap > 1)
{
/* compare [gap] with its parent */
int parent = gap / 2;
if (last < *m_items[parent]) {
m_items[gap] = m_items[parent];
gap = parent;
} else {
/* we don't need to continue upstairs */
break;
}
}
/* Heapify (move gap) down: */
while (true) {
/* where we do have our children? */
int child = gap * 2; // first child is at [parent * 2]
if (child > m_size) break;
/* choose the smaller child */
if (child < m_size && *m_items[child + 1] < *m_items[child])
child++;
/* is it smaller than our parent? */
if (!(*m_items[child] < last)) {
/* 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 */
m_items[gap] = m_items[child];
gap = child;
}
/* move parent to the proper place */
if (m_size > 0) m_items[gap] = &last;
} else {
assert(idx == m_size);
m_size--;
}
CheckConsistency();
}
template <class Titem_>
inline int CBinaryHeapT<Titem_>::FindLinear(const Titem_& item) const
{
if (IsEmpty()) return 0;
for (ItemPtr *ppI = m_items + 1, *ppLast = ppI + m_size; ppI <= ppLast; ppI++) {
if (*ppI == &item) {
return ppI - m_items;
}
}
return 0;
}
template <class Titem_>
FORCEINLINE void CBinaryHeapT<Titem_>::CheckConsistency()
{
/* enable it if you suspect binary heap doesn't work well */
#if 0
for (int child = 2; child <= m_size; child++) {
int parent = child / 2;
assert(!(*m_items[child] < *m_items[parent]));
}
#endif
}
#endif /* BINARYHEAP_HPP */
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