Add util::dfs

libs/util/include/psemek/util/dfs.hpp

@@ -0,0 +1,87 @@
+#pragma once
+
+#include <psemek/util/range.hpp>
+#include <psemek/util/resource_container.hpp>
+
+#include <cstdint>
+#include <vector>
+
+namespace psemek::util
+{
+
+	template <typename EdgesProvider, typename Index = std::uint32_t>
+	struct dfs
+	{
+		dfs(Index count, EdgesProvider edges_provider)
+			: visited_(count, visited_flag::not_visited)
+			, parent_(count, null)
+			, edges_provider_(std::move(edges_provider))
+		{}
+
+		struct cycle_iterator
+		{
+			dfs * parent;
+			Index i;
+
+			Index operator *() const { return i; }
+			cycle_iterator & operator ++()
+			{
+				i = parent->parent_[i];
+				return *this;
+			}
+
+			friend bool operator == (cycle_iterator const & i1, cycle_iterator const & i2)
+			{
+				return i1.i == i2.i;
+			}
+		};
+
+		template <typename CycleCallback>
+		void run(CycleCallback && cycle_callback)
+		{
+			for (Index i = 0; i < visited_.size(); ++i)
+				if (visited_[i] == visited_flag::not_visited)
+					step(i, cycle_callback);
+		}
+
+	private:
+		static constexpr Index null = static_cast<Index>(-1);
+
+		enum class visited_flag : std::uint8_t
+		{
+			not_visited,
+			visiting,
+			visited,
+		};
+
+		std::vector<visited_flag> visited_;
+		std::vector<Index> parent_;
+
+		EdgesProvider edges_provider_;
+
+		template <typename CycleCallback>
+		void step(Index i, CycleCallback & cycle_callback)
+		{
+			visited_[i] = visited_flag::visiting;
+
+			edges_provider_(i, [&](Index j)
+			{
+				switch (visited_[j])
+				{
+				case visited_flag::not_visited:
+					parent_[j] = i;
+					step(j, cycle_callback);
+					break;
+				case visited_flag::visiting:
+					cycle_callback(util::range{cycle_iterator{this, i}, cycle_iterator{this, null}});
+					break;
+				case visited_flag::visited:
+					break;
+				}
+			});
+
+			visited_[i] = visited_flag::visited;
+		}
+	};
+
+}