review kruskal: some refactoring + todos
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2 changed files with 44 additions and 42 deletions
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@ -2,16 +2,12 @@
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// Authors: Georǵi Kocharyan
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#include <iostream>
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#include <cstdio>
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#include <vector>
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#include <list>
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#include <queue>
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#include <algorithm>
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#include <string>
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#include <functional>
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#include "../../weighted_graph.h"
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#include <tuple>
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#include "../../weighted_graph.h"
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struct key_compare
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{
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@ -21,9 +17,18 @@
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}
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};
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void next_edge(WeightedGraph const & G, std::vector<std::list<int>> & elements, std::vector<int> component) {
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}
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struct Edge
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{
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// todo: use type alias
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int from;
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int to;
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double weight;
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bool operator<(Edge const & other) const {
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return weight < other.weight;
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}
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};
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void kruskal(WeightedGraph const & G) {
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// preprocessing: remove all double edges except the minimal ones
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@ -33,7 +38,7 @@ void kruskal(WeightedGraph const & G) {
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// preprocessing: create a vector of lists tracking the elements of the components
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std::vector<std::list<int>> elements;
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std::vector<std::vector<int>> elements;
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elements.resize(H.num_nodes());
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for (int i = 0; i < H.num_nodes(); i++)
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{
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@ -52,53 +57,49 @@ void kruskal(WeightedGraph const & G) {
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// preprocessing: create a vector containing all edges in O(m)
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// then sort them according to their weight
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// todo: use std::vector<Edge>
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std::vector<std::tuple<int, int, double>> edges;
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edges.resize(H.num_edges());
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int count = 0;
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edges.reserve(H.num_edges());
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for (int i = 0; i < H.num_nodes(); i++)
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{
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for (const auto& j : H.adjList(i))
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{
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edges[count] = std::make_tuple(i,j.first,j.second);
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count++;
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edges.emplace_back(i,j.first,j.second);
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}
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}
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std::sort(edges.begin(), edges.end(),key_compare());
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std::sort(edges.begin(), edges.end(), key_compare());
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for (const auto& edge : edges)
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{
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// check if edge connects two of the same component
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if (!(component[std::get<0>(edge)]==component[std::get<1>(edge)]))
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if (component[std::get<0>(edge)] != component[std::get<1>(edge)])
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{
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// output edge
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std::cout << std::get<0>(edge) << "-" << std::get<1>(edge) << "\t" << std::get<2>(edge) << std::endl;
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total_weight = total_weight + std::get<2>(edge);
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total_weight += std::get<2>(edge);
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// make the components of each node the same
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// the larger component absorbs the second to guarantee O(mlogn) runtime
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// todo: avoid code duplication by moving out stuff from if-else
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int moved;
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int movedto;
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if (elements[component[std::get<0>(edge)]].size() >= elements[component[std::get<1>(edge)]].size())
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{
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// move all elements of second component to first
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int moved = component[std::get<1>(edge)];
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int movedto = component[std::get<0>(edge)];
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for (const auto& node : (elements[moved]))
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{
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elements[movedto].push_back(node);
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component[node] = movedto;
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}
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elements[moved].clear();
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moved = component[std::get<1>(edge)];
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movedto = component[std::get<0>(edge)];
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}
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else
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{
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// move all elements of first component to second
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int moved = component[std::get<0>(edge)];
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int movedto = component[std::get<1>(edge)];
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for (const auto& node : (elements[moved]))
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{
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elements[movedto].push_back(node);
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component[node] = movedto;
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}
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elements[moved].clear();
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moved = component[std::get<0>(edge)];
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movedto = component[std::get<1>(edge)];
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}
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for (const auto& node : (elements[moved]))
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{
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elements[movedto].push_back(node);
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component[node] = movedto;
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}
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elements[moved].clear();
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}
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}
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@ -7,23 +7,24 @@
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struct Node {
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// todo: introduce neighbor struct and use it instead of std::pair
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std::list<std::pair<int, double>> neighbours;
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Node() = default;
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Node(std::list<std::pair<int, double>> neighbours);
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explicit Node(std::list<std::pair<int, double>> neighbours);
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void add_edge(int node_id, double weight);
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int deg() const;
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[[nodiscard]] int deg() const;
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};
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class WeightedGraph {
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public:
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WeightedGraph(size_t num_nodes);
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explicit WeightedGraph(size_t num_nodes);
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void add_edge(int from, int to, double weight);
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std::list<std::pair<int, double>> adjList(int node_id) const;
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size_t num_nodes() const;
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int num_edges() const;
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int deg(int v) const;
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std::pair<int,double> min_neighbour(int node_id) const;
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WeightedGraph remove_parallel() const;
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[[nodiscard]] std::list<std::pair<int, double>> adjList(int node_id) const;
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[[nodiscard]] size_t num_nodes() const;
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[[nodiscard]] int num_edges() const;
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[[nodiscard]] int deg(int v) const;
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[[nodiscard]] std::pair<int,double> min_neighbour(int node_id) const;
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[[nodiscard]] WeightedGraph remove_parallel() const;
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private:
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std::vector<Node> nodes;
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