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#pragma once
#include <unordered_map>
#include <unordered_set>
namespace vcpkg::Graphs
{
enum class ExplorationStatus
{
// We have not visited this vertex
NOT_EXPLORED,
// We have visited this vertex but haven't visited all vertices in its subtree
PARTIALLY_EXPLORED,
// We have visited this vertex and all vertices in its subtree
FULLY_EXPLORED
};
template<class V, class U>
__interface AdjacencyProvider
{
std::vector<V> adjacency_list(const U& vertex) const;
U load_vertex_data(const V& vertex) const;
};
template<class V, class U>
static void topological_sort_internal(const V& vertex,
const AdjacencyProvider<V, U>& f,
std::unordered_map<V, ExplorationStatus>& exploration_status,
std::vector<U>& sorted)
{
ExplorationStatus& status = exploration_status[vertex];
switch (status)
{
case ExplorationStatus::FULLY_EXPLORED: return;
case ExplorationStatus::PARTIALLY_EXPLORED: Checks::exit_with_message(VCPKG_LINE_INFO, "cycle in graph");
case ExplorationStatus::NOT_EXPLORED:
{
status = ExplorationStatus::PARTIALLY_EXPLORED;
U vertex_data = f.load_vertex_data(vertex);
for (const V& neighbour : f.adjacency_list(vertex_data))
topological_sort_internal(neighbour, f, exploration_status, sorted);
sorted.push_back(std::move(vertex_data));
status = ExplorationStatus::FULLY_EXPLORED;
return;
}
default: Checks::unreachable(VCPKG_LINE_INFO);
}
}
template<class V, class U>
std::vector<U> topological_sort(const std::vector<V>& starting_vertices, const AdjacencyProvider<V, U>& f)
{
std::vector<U> sorted;
std::unordered_map<V, ExplorationStatus> exploration_status;
for (auto& vertex : starting_vertices)
{
topological_sort_internal(vertex, f, exploration_status, sorted);
}
return sorted;
}
template<class V>
struct GraphAdjacencyProvider final : AdjacencyProvider<V, V>
{
const std::unordered_map<V, std::unordered_set<V>>& vertices;
GraphAdjacencyProvider(const std::unordered_map<V, std::unordered_set<V>>& vertices) : vertices(vertices) {}
std::vector<V> adjacency_list(const V& vertex) const override
{
const std::unordered_set<V>& as_set = this->vertices.at(vertex);
return std::vector<V>(as_set.cbegin(), as_set.cend()); // TODO: Avoid redundant copy
}
V load_vertex_data(const V& vertex) const override { return vertex; }
};
template<class V>
struct Graph
{
public:
void add_vertex(V v) { this->vertices[v]; }
// TODO: Change with iterators
void add_vertices(const std::vector<V>& vs)
{
for (const V& v : vs)
{
this->vertices[v];
}
}
void add_edge(V u, V v)
{
this->vertices[v];
this->vertices[u].insert(v);
}
std::vector<V> topological_sort() const
{
GraphAdjacencyProvider<V> adjacency_provider{this->vertices};
std::unordered_map<V, int> indegrees = count_indegrees();
std::vector<V> sorted;
sorted.reserve(indegrees.size());
std::unordered_map<V, ExplorationStatus> exploration_status;
exploration_status.reserve(indegrees.size());
for (auto& pair : indegrees)
{
if (pair.second == 0) // Starting from vertices with indegree == 0. Not required.
{
V vertex = pair.first;
topological_sort_internal(vertex, adjacency_provider, exploration_status, sorted);
}
}
return sorted;
}
std::unordered_map<V, int> count_indegrees() const
{
std::unordered_map<V, int> indegrees;
for (auto& pair : this->vertices)
{
indegrees[pair.first];
for (V neighbour : pair.second)
{
++indegrees[neighbour];
}
}
return indegrees;
}
const std::unordered_map<V, std::unordered_set<V>>& adjacency_list() const { return this->vertices; }
std::vector<V> vertex_list() const
{
// why no &? it returns 0
std::vector<V> vertex_list;
for (const auto& vertex : this->vertices)
{
vertex_list.emplace_back(vertex.first);
}
return vertex_list;
}
private:
std::unordered_map<V, std::unordered_set<V>> vertices;
};
}
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