OpenTTD-patches/yapf/binaryheap.hpp

229 lines
5.9 KiB
C++

/* $Id$ */
#ifndef BINARYHEAP_HPP
#define BINARYHEAP_HPP
//void* operator new (size_t size, void* p) {return p;}
#if defined(_MSC_VER) && (_MSC_VER >= 1400)
//void operator delete (void* p, void* p2) {}
#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) 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-then' 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 = 102400)
: m_size(0)
, m_max_size(max_items)
{
m_items = new ItemPtr[max_items + 1];
}
~CBinaryHeapT()
{
Clear();
delete [] 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.
* @return false if the queue is full. */
bool 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 bool CBinaryHeapT<Titem_>::Push(Titem_& new_item)
{
if (IsFull()) return false;
// 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();
return true;
}
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 */