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/* Copyright (c) 1997-2024
Ewgenij Gawrilow, Michael Joswig, and the polymake team
Technische Universität Berlin, Germany
https://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.
--------------------------------------------------------------------------------
*/
#pragma once
#include "polymake/graph/DijkstraShortestPathBase.h"
namespace polymake {
namespace graph {
class DijkstraShortestPathWithSiblings
: public DijkstraShortestPathBase {
public:
using base_layer = DijkstraShortestPathBase;
template <typename FullLabel>
struct Label : public base_layer::Label<FullLabel> {
using base_t = base_layer::Label<FullLabel>;
using base_layer::Label<FullLabel>::Label;
//! another label on the same node merged into this one and not propagated further
FullLabel* sibling = nullptr;
//! label has been updated when absorbing a sibling
bool is_updated = false;
};
struct LabelComparatorWithUpdates : public LabelCostComparator {
template <typename FullLabel>
pm::cmp_value operator() (const FullLabel& l1, const FullLabel& l2) const
{
const pm::cmp_value cmp_cost = operations::cmp::operator()(l1.get_min_cost(), l2.get_min_cost());
if (cmp_cost != pm::cmp_eq) return cmp_cost;
// an updated label should appear first at the heap top
return l1.is_updated == l2.is_updated ? pm::cmp_eq : l1.is_updated ? pm::cmp_lt : pm::cmp_gt;
}
};
template <typename Top>
class Data : public base_layer::template Data<Top> {
public:
using base_t = typename base_layer::template Data<Top>;
using typename base_t::label_t;
using label_comparator_t = typename Top::label_comparator_t;
using base_layer::template Data<Top>::Data;
label_t* rotate_siblings(Int node)
{
label_t* old_first_label = this->labels_on_node[node];
label_t* first_sibling = old_first_label->sibling;
old_first_label->sibling = nullptr;
label_t* next_sibling = first_sibling;
while (next_sibling->sibling) next_sibling = next_sibling->sibling;
next_sibling->sibling = old_first_label;
this->labels_on_node[node] = first_sibling;
return first_sibling;
}
};
template <typename Top>
class Algo : public base_layer::template Algo<Top> {
public:
using base_t = typename base_layer::template Algo<Top>;
using typename base_t::graph_t;
using typename base_t::label_t;
using typename base_t::data_t;
void propagate(label_t* const pred_label, const Int cur_node, const Int edge_id) const
{
label_t* cur_label = this->data.labels_on_node[cur_node];
label_t* new_label = this->top().construct_label(pred_label, cur_node, edge_id);
if (cur_label) {
switch (this->top().compare_labels(new_label, cur_label)) {
case DijkstraLabelCmp::discard_new:
this->data.reclaim_label(new_label);
return;
case DijkstraLabelCmp::discard_old_and_siblings:
this->top().drop_label(cur_label);
this->top().erase_label(cur_label);
break;
case DijkstraLabelCmp::replace_old:
this->top().drop_label(cur_label);
new_label->sibling = cur_label;
break;
case DijkstraLabelCmp::discard_old_keep_siblings:
this->top().drop_label(cur_label);
new_label->sibling = cur_label->sibling;
base_t::erase_label(cur_label);
break;
case DijkstraLabelCmp::keep_new_update_old:
this->top().add_sibling(cur_label, new_label, pred_label);
if (cur_label->heap_pos < 0) {
cur_label->is_updated = true;
this->data.heap.push(cur_label);
}
return;
case DijkstraLabelCmp::keep_new_as_sibling:
this->top().add_sibling(cur_label, new_label, pred_label);
return;
case DijkstraLabelCmp::propagate_both:
throw std::runtime_error("DijkstraShortestPathWithSiblings: independent labels not supported yet");
}
}
this->top().push_new_label(new_label, pred_label);
}
bool process_popped(label_t* const pred_label, const bool backward) const
{
if (pred_label->is_updated) {
pred_label->is_updated = false;
if (backward) {
for (auto edge_it = entire(this->data.G.in_edges(pred_label->node)); !edge_it.at_end(); ++edge_it)
propagate_update(pred_label, edge_it.from_node(), *edge_it);
} else {
for (auto edge_it = entire(this->data.G.out_edges(pred_label->node)); !edge_it.at_end(); ++edge_it)
propagate_update(pred_label, edge_it.to_node(), *edge_it);
}
return false;
}
return true;
}
void add_sibling(label_t* cur_label, label_t* new_label, label_t* pred_label) const
{
new_label->set_predecessor(pred_label);
new_label->refc = 1;
new_label->sibling = cur_label->sibling;
cur_label->sibling = new_label;
}
void update_siblings(label_t* label) const
{
remove_redundant_siblings(label, label, this->top().is_redundant_sibling_after_update());
}
void erase_label(label_t* label) const
{
do {
label_t* sibling = label->sibling;
base_t::erase_label(label);
label = sibling;
} while (label);
}
template <typename Predicate>
void remove_redundant_siblings(label_t* const new_label, label_t* prev_sibling, const Predicate& is_redundant) const
{
label_t* cur_sibling = prev_sibling->sibling;
while (cur_sibling) {
label_t* next_sibling = cur_sibling->sibling;
if (is_redundant(new_label, cur_sibling)) {
base_t::erase_label(cur_sibling);
prev_sibling->sibling = next_sibling;
} else {
prev_sibling = cur_sibling;
}
cur_sibling = next_sibling;
}
}
protected:
using base_layer::template Algo<Top>::Algo;
void propagate_update(label_t* const pred_label, const Int cur_node, const Int edge_id) const
{
label_t* cur_label = this->data.labels_on_node[cur_node];
// an update of pred_label can have an effect only when there is a descendant label at the current node
for (label_t* any_label = cur_label; ; any_label = any_label->sibling) {
if (any_label) {
if (any_label->predecessor == pred_label) break;
} else {
return;
}
}
if (this->top().update_label(pred_label, cur_label, edge_id)) {
this->top().update_siblings(cur_label);
if (cur_label->heap_pos < 0) {
cur_label->is_updated = true;
this->data.heap.push(cur_label);
}
}
}
};
};
} }
// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
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