Class: RGL::DijkstraAlgorithm

Inherits:
Object
  • Object
show all
Defined in:
lib/rgl/dijkstra.rb

Overview

This class implements Graph#dijkstra_shortest_path and Graph#dijkstra_shortest_paths

Constant Summary collapse

DEFAULT_DISTANCE_COMBINATOR =

Distance combinator is a lambda that accepts the distance (usually from the source) to vertex u and the weight of the edge connecting vertex u to another vertex v and returns the distance to vertex v if it’s reached through the vertex u. By default, the distance to vertex u and the edge’s weight are summed.

lambda { |distance, edge_weight| distance + edge_weight }

Instance Method Summary collapse

Constructor Details

#initialize(graph, edge_weights_map, visitor, distance_combinator = nil) ⇒ DijkstraAlgorithm

Initializes Dijkstra’s algorithm for a graph with provided edges weights map.



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# File 'lib/rgl/dijkstra.rb', line 19

def initialize(graph, edge_weights_map, visitor, distance_combinator = nil)
  @graph               = graph
  @edge_weights_map    = build_edge_weights_map(edge_weights_map)
  @visitor             = visitor
  @distance_combinator = distance_combinator || DEFAULT_DISTANCE_COMBINATOR
end

Instance Method Details

#find_shortest_paths(source) ⇒ Object

Finds the shortest path from the source to every other vertex.



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# File 'lib/rgl/dijkstra.rb', line 48

def find_shortest_paths(source)
  init(source)
  relax_edges
end

#shortest_path(source, target) ⇒ Object

Finds the shortest path from the source to the target in the graph.

Returns the shortest path, if it exists, as an Array of vertices. Otherwise, returns nil.



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# File 'lib/rgl/dijkstra.rb', line 30

def shortest_path(source, target)
  init(source)
  relax_edges(target, true)
  PathBuilder.new(source, @visitor.parents_map).path(target)
end

#shortest_paths(source) ⇒ Object

Finds the shortest path form the source to every other vertex of the graph and builds shortest paths map.

Returns the shortest paths map that contains the shortest path (if it exists) from the source to any vertex of the graph.



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# File 'lib/rgl/dijkstra.rb', line 41

def shortest_paths(source)
  find_shortest_paths(source)
  PathBuilder.new(source, @visitor.parents_map).paths(@graph.vertices)
end