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authorchriseth <chris@ethereum.org>2018-03-16 02:53:29 +0800
committerAlex Beregszaszi <alex@rtfs.hu>2018-04-03 22:29:18 +0800
commiteb5b18e8145d7d3971c450ba220f322e5f66d45c (patch)
tree19efd096e8c7ac0761a3f38279c75ecf5fb1d273 /libdevcore
parent5bdadff0d8a9c32745dd46aa639283718613efdc (diff)
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Generalize cycle detection.
Diffstat (limited to 'libdevcore')
-rw-r--r--libdevcore/Algorithms.h76
1 files changed, 76 insertions, 0 deletions
diff --git a/libdevcore/Algorithms.h b/libdevcore/Algorithms.h
new file mode 100644
index 00000000..b2540668
--- /dev/null
+++ b/libdevcore/Algorithms.h
@@ -0,0 +1,76 @@
+/*
+ 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:
+ /// 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(std::function<void(V const&, CycleDetector&)> _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--;
+ if (m_firstCycleVertex && m_depth == 1)
+ m_firstCycleVertex = &_vertex;
+
+ m_processing.erase(&_vertex);
+ m_processed.insert(&_vertex);
+ return m_firstCycleVertex;
+ }
+
+private:
+ std::function<void(V const&, CycleDetector&)> m_visit;
+ std::set<V const*> m_processing;
+ std::set<V const*> m_processed;
+ size_t m_depth = 0;
+ V const* m_firstCycleVertex = nullptr;
+};
+
+}