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#include "../../Seminar12/src/graph_impl/weighted_graph/weighted_graph.h"
#include <queue>
#include <iostream>
#include <limits.h>
using vertex_t = weighted_graph::vertex_t;
using vertex_index_t = weighted_graph::vertex_index_t;
using weight_t = weighted_graph::weight_t;
struct mst_info
{
std::vector<vertex_index_t> tree;
int cost = 0;
};
mst_info prim(const weighted_graph& g, vertex_index_t start = 0)
{
mst_info result;
if(g.vertex_count() == 0)
return result;
std::vector<bool> visited(g.vertex_count(), false);
result.tree.resize(g.vertex_count(), -1);
// min_cost[i] = minimum cost found!
std::vector<weight_t> min_cost(g.vertex_count(), INT_MAX);
struct vertex_comparator
{
bool operator()(const vertex_t& lhs, const vertex_t& rhs) const
{
return lhs.second > rhs.second;
}
};
std::priority_queue<vertex_t, std::vector<vertex_t>, vertex_comparator> p;
// initialize structures:
p.push({start, 0});
min_cost[start] = 0;
size_t found_edges = 0;
while(found_edges != g.vertex_count())
{
vertex_index_t current_vertex = p.top().first;
weight_t current_weight = p.top().second;
p.pop();
if(visited[current_vertex])
continue;
visited[current_vertex] = true;
result.cost += current_weight;
++found_edges;
const auto& adjacent = g.adjacent(current_vertex);
for(const vertex_t& vertex : adjacent)
{
vertex_index_t found_index = vertex.first;
weight_t found_weight = vertex.second;
if(!visited[found_index] && found_weight < min_cost[found_index])
{
result.tree[found_index] = current_vertex;
p.push({found_index, found_weight});
min_cost[found_index] = found_weight;
}
}
}
return result;
}
int main()
{
weighted_graph g(7, false);
g.add_edge(0, 1, 4);
g.add_edge(0, 2, 3);
g.add_edge(1, 2, 1);
g.add_edge(1, 3, 2);
g.add_edge(2, 4, 5);
g.add_edge(3, 4, 6);
g.add_edge(3, 5, 7);
g.add_edge(4, 6, 8);
g.add_edge(5, 6, 4);
auto result = prim(g);
std::cout << "Total cost of MST: " << result.cost << '\n';
std::cout << "Tree structure (parent array): ";
for (const auto x : result.tree)
{
std::cout << x << " ";
}
std::cout << '\n';
return 0;
}
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