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/*
This file is part of solidity.
solidity 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 3 of the License, or
(at your option) any later version.
solidity 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.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
#include <functional>
#include <set>
namespace dev
{
/**
* Detector for cycles in directed graphs. It returns the first
* vertex on the path towards a cycle or a nullptr if there is
* no reachable cycle starting from a given vertex.
*/
template <typename V>
class CycleDetector
{
public:
using Visitor = std::function<void(V const&, CycleDetector&, size_t)>;
/// Initializes the cycle detector
/// @param _visit function that is given the current vertex
/// and is supposed to call @a run on all
/// adjacent vertices.
explicit CycleDetector(Visitor _visit):
m_visit(std::move(_visit))
{ }
/// Recursively perform cycle detection starting
/// (or continuing) with @param _vertex
/// @returns the first vertex on the path towards a cycle from @a _vertex
/// or nullptr if no cycle is reachable from @a _vertex.
V const* run(V const& _vertex)
{
if (m_firstCycleVertex)
return m_firstCycleVertex;
if (m_processed.count(&_vertex))
return nullptr;
else if (m_processing.count(&_vertex))
return m_firstCycleVertex = &_vertex;
m_processing.insert(&_vertex);
m_depth++;
m_visit(_vertex, *this, m_depth);
m_depth--;
if (m_firstCycleVertex && m_depth == 1)
m_firstCycleVertex = &_vertex;
m_processing.erase(&_vertex);
m_processed.insert(&_vertex);
return m_firstCycleVertex;
}
private:
Visitor m_visit;
std::set<V const*> m_processing;
std::set<V const*> m_processed;
size_t m_depth = 0;
V const* m_firstCycleVertex = nullptr;
};
}
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