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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/GenericGraph.h"
#include "polymake/graph/graph_iterators.h"
namespace polymake { namespace graph {
class NodeDistances {
protected:
std::vector<Int> dist;
public:
static const bool visit_all_edges=false;
NodeDistances() {}
template <typename TGraph>
explicit NodeDistances(const GenericGraph<TGraph>& G)
: dist(G.top().dim(), -1) {}
template <typename TGraph>
void clear(const GenericGraph<TGraph>& G)
{
std::fill(dist.begin(), dist.end(), -1);
}
bool operator()(Int n)
{
dist[n] = 0;
return true;
}
bool operator()(Int n_from, Int n_to)
{
if (dist[n_to] < 0) {
dist[n_to] = dist[n_from]+1;
return true;
}
return false;
}
Int operator[] (Int n) const { return dist[n]; }
};
/// Determine the diameter of a graph.
template <typename TGraph>
Int diameter(const GenericGraph<TGraph>& G)
{
BFSiterator<TGraph, VisitorTag<NodeDistances>> it(G);
Int diam = 0;
for (auto n = entire(nodes(G)); !n.at_end(); ++n) {
for (it.reset(*n); it.undiscovered_nodes()>0; ++it) ;
assign_max(diam, it.node_visitor()[it.get_queue().back()]);
}
return diam;
}
} }
// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
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