AU: Tarjan's algorithm.

src/platform/update_engine/tarjan.h

Index: src/platform/update_engine/tarjan.h
diff --git a/src/platform/update_engine/tarjan.h b/src/platform/update_engine/tarjan.h
new file mode 100644
index 0000000000000000000000000000000000000000..1a80a95d56fd9fe385091d638ce37e531facdac6
--- /dev/null
+++ b/src/platform/update_engine/tarjan.h
@@ -0,0 +1,39 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_TARJAN_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_TARJAN_H__
+
+// This is an implemenation of Tarjan's algorithm which finds all
+// Strongly Connected Components in a graph.
+
+// Note: a true Tarjan algorithm would find all strongly connected components
+// in the graph. This implementation will only find the strongly connected
+// component containing the vertex passed in.
+
+#include <vector>
+#include "update_engine/graph_types.h"
+
+namespace chromeos_update_engine {
+
+class TarjanAlgorithm {
+ public:
+  TarjanAlgorithm() : index_(0), required_vertex_(0) {}
+
+  // 'out' is set to the result if there is one, otherwise it's untouched.
+  void Execute(Vertex::Index vertex,
+               Graph* graph,
+               std::vector<Vertex::Index>* out);
+ private:
+  void Tarjan(Vertex::Index vertex, Graph* graph);
+
+  Vertex::Index index_;
+  Vertex::Index required_vertex_;
+  std::vector<Vertex::Index> stack_;
+  std::vector<std::vector<Vertex::Index> > components_;
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_TARJAN_H__