/usr/include/polymake/Heap.h is in libpolymake-dev-common 3.2r2-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Ewgenij Gawrilow, Michael Joswig (Technische Universitaet Berlin, Germany)
http://www.polymake.org
This program 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; either version 2, or (at your option) any
later version: http://www.gnu.org/licenses/gpl.txt.
This program 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.
--------------------------------------------------------------------------------
*/
#ifndef POLYMAKE_HEAP_H
#define POLYMAKE_HEAP_H
#include "polymake/vector"
#include "polymake/internal/comparators.h"
#include <cassert>
namespace pm {
/** Heap (priority queue).
The queue is stored in a dynamic array, with element indices inducing an implicit binary tree structure
(the child elements of the i-th element have indices 2*i+1 and 2*i+2.)
\tparam Policy class defining the data types and housekeeping methods:
value_type
elements stored in the queue
key_type
comparison keys associated with elements
key_comparator_type
comparator for the keys
int position(value_type) const
current position (index) of the element in the heap
void update_position(value_type, int old, int new)
change the current position of stored in/with the element; -1 on any side means "none"
key_type key(value_type)
retrieve the key of the element
key_comparator_type key_comparator() const
retrieve the key comparator object
keys, values, and comparator may be passed and/or returned by const reference if desired
*/
template <typename Policy>
class Heap : public Policy {
public:
typedef typename Policy::value_type value_type;
typedef typename Policy::key_type key_type;
typedef typename Policy::key_comparator_type key_comparator_type;
typedef std::vector<value_type> queue_t;
/** Create an empty heap
@param expected_qlen expected maximal heap size (helps to avoid extra reallocations)
*/
explicit Heap(const Policy& policy_init, size_t expected_qlen=0)
: Policy(policy_init)
{
if (expected_qlen>0) queue.reserve(expected_qlen);
}
const queue_t& get_queue() const { return queue; }
bool empty() const { return queue.empty(); }
void clear() { queue.clear(); }
/// Add a new element or update the position of the existing one after a key increase/decrease.
void push(const value_type& elem);
/// The currently topmost element
const value_type& top() const { return queue.front(); }
/// Sift the topmost element down if its key has been increased.
void update_top()
{
sift_down(0, 0, 0);
}
/// Remove the topmost element and return it, adjust the heap
value_type pop()
{
assert(!queue.empty());
value_type top=queue.front();
assert(this->position(top)==0);
sift_down(queue.size()-1, 0, 1);
queue.pop_back();
this->update_position(top, 0, -1);
return top;
}
/// Remove the element
void erase(const value_type& elem)
{
erase(this->position(elem));
}
/// Remove element at the given queue position
value_type erase_at(int pos);
private:
/// @param new_pos where to start looking for the new position
void sift_down(int old_pos, int pos, int shrinking);
queue_t queue;
#if POLYMAKE_DEBUG
public:
bool sanity_check() const;
#endif
};
template <typename Policy>
void Heap<Policy>::push(const value_type& elem)
{
const int old_pos=this->position(elem);
bool moved=false;
int pos=old_pos;
if (old_pos < 0) {
pos=queue.size();
queue.push_back(elem);
} else {
assert(size_t(old_pos)<queue.size() && queue[old_pos]==elem);
}
const key_type& k=this->key(elem);
const key_comparator_type& cmp=this->key_comparator();
while (pos>0) {
const int p_pos=(pos-1)/2;
const key_type& p_k=this->key(queue[p_pos]); // parent node in the heap tree
if (cmp(p_k, k) <= 0) break;
this->update_position(queue[pos]=queue[p_pos], p_pos, pos);
pos=p_pos;
moved=true;
}
if (moved) {
queue[pos]=elem;
this->update_position(elem, old_pos, pos);
} else if (old_pos>=0) {
sift_down(old_pos, old_pos, 0);
} else {
this->update_position(elem, old_pos, pos);
}
}
template <typename Policy>
void Heap<Policy>::sift_down(int old_pos, int pos, int shrinking)
{
const int end=queue.size()-shrinking;
const key_type& k=this->key(queue[old_pos]);
const key_comparator_type& cmp=this->key_comparator();
int c_pos;
while ((c_pos=2*pos+1) < end) {
if (c_pos+1 < end &&
cmp(this->key(queue[c_pos+1]), this->key(queue[c_pos])) < 0) ++c_pos;
if (cmp(k, this->key(queue[c_pos])) <= 0) break;
this->update_position(queue[pos]=queue[c_pos], c_pos, pos);
pos=c_pos;
}
if (pos != old_pos) {
this->update_position(queue[pos]=queue[old_pos], old_pos, pos);
}
}
template <typename Policy>
typename Policy::value_type Heap<Policy>::erase_at(int pos)
{
const value_type v=queue[pos];
this->update_position(v, pos, -1);
const int last_q=queue.size()-1;
if (pos < last_q) {
const key_type& k=this->key(queue.back());
const key_comparator_type& cmp=this->key_comparator();
bool bubble_up=false;
int p_pos;
while ((p_pos=(pos-1)/2) > 0) {
if (cmp(k, this->key(queue[p_pos])) >= 0) break;
this->update_position(queue[pos]=queue[p_pos], p_pos, pos);
bubble_up=true;
pos=p_pos;
}
if (bubble_up)
this->update_position(queue[pos]=queue.back(), last_q, pos);
else
sift_down(last_q, pos, 1);
}
queue.pop_back();
return v;
}
#if POLYMAKE_DEBUG
template <typename Policy>
bool Heap<Policy>::sanity_check() const
{
bool OK=true;
for (int i=0, iend=queue.size(); i<iend; ++i) {
const value_type& el=queue[i];
const int pos=this->position(el);
if (pos != i) {
std::cerr << "check(Heap): elem " << el << " has wrong index " << pos << " instead of " << i << std::endl;
OK=false;
}
if (i>0) {
int p=(i-1)/2;
if (this->key_comparator()(this->key(el), this->key(queue[p]))<0) {
std::cerr << "check(Heap): parent(" << el << ")=" << p << std::endl;
OK=false;
}
}
}
return OK;
}
#endif
} // end namespace pm
namespace polymake {
using pm::Heap;
}
#endif // POLYMAKE_HEAP_H
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