// This may look like C code, but it is really -*- C++ -*-
/* 
Copyright (C) 1988 Free Software Foundation
    written by Dirk Grunwald (grunwald@cs.uiuc.edu)
    adapted for libg++ by Doug Lea (dl@rocky.oswego.edu)

This file is part of the GNU C++ Library.  This library is free
software; you can redistribute it and/or modify it under the terms of
the GNU Library General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.  This library 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 Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free Software
Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/


#ifdef __GNUG__
#pragma implementation
#endif
#include <limits.h>
#include "<T>.PHPQ.h"

//
//	This defines a Pairing Heap structure
//
//	See ``The Pairing Heap: A New Form of Self-Adjusting Heap''
//	Fredman, Segdewick et al,
//	Algorithmica (1986) 1:111-129
//
//	In particular, this implements the pairing heap using the circular
//	list.
//
//

<T>PHPQ::<T>PHPQ(int sz)
{
  storage = 0;
  root = 0;
  count = 0;
  size = 0;
  prealloc(sz);
}

<T>PHPQ::<T>PHPQ(<T>PHPQ& a)
{
  storage = 0;
  root  = 0;
  count = 0;
  size = 0;
  prealloc(a.size);
  for (Pix i = a.first(); i != 0; a.next(i)) enq(a(i));
}


void <T>PHPQ::prealloc(int newsize)
{
  ++newsize; // leave a spot for freelist
  if (size != 0)
  {
    int news = size;
    while (news <= newsize) news = (news * 3) / 2;
    newsize = news;
  }
  // see if indices are OK
  <T>PHPQNode test;
  test.sibling = 0;
  test.sibling = ~test.sibling;
  if ((unsigned long)newsize > (unsigned long)(test.sibling))
    error("storage size exceeds index range");

  if (storage == 0)
  {
    storage = new <T>PHPQNode[size = newsize];
    for (int i = 0; i < size; ++i) 
    {
      storage[i].sibling = i + 1;
      storage[i].valid = 0;
    }
    storage[size-1].sibling = 0;
  }
  else
  {
    <T>PHPQNode* newstor = new <T>PHPQNode[newsize];
    for (int i = 1; i < size; ++i)
      newstor[i] = storage[i];
    delete [] storage;
    storage = newstor;
    for (i = size; i < newsize; ++i) 
    {
      storage[i].sibling = i + 1;
      storage[i].valid = 0;
    }
    storage[newsize-1].sibling = 0;
    storage[0].sibling = size;
    size = newsize;
  }
}


void <T>PHPQ::clear()
{
  for (int i = 0; i < size; ++i) 
  {
    storage[i].sibling = i + 1;
    storage[i].valid = 0;
  }
  storage[size-1].sibling = 0;
  root = 0;
  count = 0;
}

Pix <T>PHPQ::enq(<T&> item)
{
  ++count;
  if (storage[0].sibling == 0)
    prealloc(count);

  int cell = storage[0].sibling;
  storage[0].sibling = storage[cell].sibling;
  storage[cell].sibling = 0;
  storage[cell].children = 0;
  storage[cell].item = item;
  storage[cell].valid = 1;
  
  if (root == 0) 
  {
    root = cell;
    return Pix(root);
  }
  else 
  {
    int parent;
    int child;
    
    if (<T>LE(storage[root].item, storage[cell].item))
    {
      parent = root; child = cell;
    } 
    else 
    {
      parent = cell; child = root;
    }
    int popsKid = storage[parent].children;
    
    if (popsKid == 0) 
    {
      storage[parent].children = child;
      storage[child].sibling = child;
    } 
    else 
    {
      int temp = storage[popsKid].sibling;
      storage[popsKid].sibling = child;
      storage[child].sibling = temp;
      storage[parent].children = child;
    }
    root = parent;
    return Pix(cell);
  }
}

//
//	Item removal is the most complicated routine.
//
//	We remove the root (should there be one) and then select a new
//	root. The siblings of the root are in a circular list. We continue
//	to pair elements in this list until there is a single element.
//	This element will be the new root.

void <T>PHPQ::del_front()
{
  int valid = 0;
  do 
  {
    if (root == 0) return;
	if (valid = storage[root].valid)
      --count;
    storage[root].valid = 0;
	int child = storage[root].children;
    storage[root].sibling = storage[0].sibling;
    storage[0].sibling = root;

	if (child == 0)
    {
      root = 0;
      return;
    }
    else 
    {
      while(storage[child].sibling != child) 
      {
		// We have at least two kids, but we may only have
		// two kids. So, oneChild != child, but it is possible
		// that twoChild == child.
        
		int oneChild = storage[child].sibling;
		int twoChild = storage[oneChild].sibling;

		// Remove the two from the sibling list

		storage[child].sibling = storage[twoChild].sibling;
		storage[oneChild].sibling = 0;
		storage[twoChild].sibling = 0;
		
        int bestChild;
        int worstChild;
    
        if (<T>LE(storage[oneChild].item, storage[twoChild].item))
        {
          bestChild = oneChild; worstChild = twoChild;
        } 
        else 
        {
          bestChild = twoChild; worstChild = oneChild;
        }
        int popsKid = storage[bestChild].children;
        
        if (popsKid == 0) 
        {
          storage[bestChild].children = worstChild;
          storage[worstChild].sibling = worstChild;
        } 
        else 
        {
          int temp = storage[popsKid].sibling;
          storage[popsKid].sibling = worstChild;
          storage[worstChild].sibling = temp;
          storage[bestChild].children = worstChild;
        }
		if (twoChild == child) 
        {
          // We have reduced the two to one, so we'll be exiting.
          child = bestChild;
          storage[child].sibling = child;
        } 
        else 
        {
          // We've removed two siblings, now we need to insert
          // the better of the two
          storage[bestChild].sibling = storage[child].sibling;
          storage[child].sibling = bestChild;
          child = storage[bestChild].sibling;
		}
      }
      root = child;
	}
  } while ( !valid );
}

void <T>PHPQ::del(Pix p) 
{
  if (p == 0) error("null Pix");
  int i = int(p);
  if (storage[i].valid)
  {
    if (i == root)
      del_front();
    else
    {
      storage[i].valid = 0;
      --count;
    }
  }
}


Pix <T>PHPQ::seek(<T&> key)
{
  for (int i = 1; i < size; ++i)
    if (storage[i].valid && <T>EQ(storage[i].item, key))
      return Pix(i);
  return 0;
}

Pix <T>PHPQ::first()
{
  for (int i = 1; i < size; ++i)
    if (storage[i].valid)
      return Pix(i);
  return 0;
}


void <T>PHPQ::next(Pix& p)
{
  if (p == 0) return;
  for (int i = int(p)+1; i < size; ++i)
    if (storage[i].valid)
    {
      p = Pix(i); 
      return;
    }
  p = 0;
}

int <T>PHPQ::OK()
{
  int v = storage != 0;
  int n = 0;
  for (int i = 0; i < size; ++i) if (storage[i].valid) ++n;
  v &= n == count;
  v &= check_sibling_list(root);
  int ct = LONG_MAX;
  n = 0;
  int f = storage[0].sibling;
  while (f != 0 && ct-- > 0)
  {
    f = storage[f].sibling;
    ++n;
  }
  v &= ct > 0;
  v &= n <= size - count;
  if (!v) error("invariant failure");
  return v;
}


int <T>PHPQ::check_sibling_list(int t)
{
  if (t != 0)
  {
    int s = t;
    long ct = LONG_MAX;      // Lots of chances to find self!
    do 
    {
      if (storage[s].valid && !check_sibling_list(storage[s].children))
        return 0;
      s = storage[s].sibling;
    } while (ct-- > 0 && s != t && s != 0);
    if (ct <= 0) return 0;
  }
  return 1;
}


