class RGL::DijkstraAlgorithm
Constants
- 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.
Public Class Methods
Initializes Dijkstra's algorithm for a graph with provided edges weights map.
# File lib/rgl/dijkstra.rb 18 def initialize(graph, edge_weights_map, visitor, distance_combinator = nil) 19 @graph = graph 20 @edge_weights_map = build_edge_weights_map(edge_weights_map) 21 @visitor = visitor 22 @distance_combinator = distance_combinator || DEFAULT_DISTANCE_COMBINATOR 23 end
Public Instance Methods
Finds the shortest path from the source to every other vertex.
# File lib/rgl/dijkstra.rb 47 def find_shortest_paths(source) 48 init(source) 49 relax_edges 50 end
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.
# File lib/rgl/dijkstra.rb 29 def shortest_path(source, target) 30 init(source) 31 relax_edges(target, true) 32 PathBuilder.new(source, @visitor.parents_map).path(target) 33 end
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.
# File lib/rgl/dijkstra.rb 40 def shortest_paths(source) 41 find_shortest_paths(source) 42 PathBuilder.new(source, @visitor.parents_map).paths(@graph.vertices) 43 end
Private Instance Methods
# File lib/rgl/dijkstra.rb 100 def build_edge_weights_map(edge_weights_map) 101 edge_weights_map.is_a?(EdgePropertiesMap) ? edge_weights_map : NonNegativeEdgePropertiesMap.new(edge_weights_map, @graph.directed?) 102 end
# File lib/rgl/dijkstra.rb 54 def init(source) 55 @visitor.set_source(source) 56 57 @queue = MinPriorityQueue.new 58 @queue.push(source, 0) 59 end
# File lib/rgl/dijkstra.rb 78 def relax_edge(u, v) 79 @visitor.handle_examine_edge(u, v) 80 81 new_v_distance = @distance_combinator.call(@visitor.distance_map[u], @edge_weights_map.edge_property(u, v)) 82 83 if new_v_distance < @visitor.distance_map[v] 84 @visitor.distance_map[v] = new_v_distance 85 @visitor.parents_map[v] = u 86 87 if @visitor.color_map[v] == :WHITE 88 @visitor.color_map[v] = :GRAY 89 @queue.push(v, new_v_distance) 90 elsif @visitor.color_map[v] == :GRAY 91 @queue.decrease_key(v, new_v_distance) 92 end 93 94 @visitor.handle_edge_relaxed(u, v) 95 else 96 @visitor.handle_edge_not_relaxed(u, v) 97 end 98 end
# File lib/rgl/dijkstra.rb 61 def relax_edges(target = nil, break_on_target = false) 62 until @queue.empty? 63 u = @queue.pop 64 65 break if break_on_target && u == target 66 67 @visitor.handle_examine_vertex(u) 68 69 @graph.each_adjacent(u) do |v| 70 relax_edge(u, v) unless @visitor.finished_vertex?(v) 71 end 72 73 @visitor.color_map[u] = :BLACK 74 @visitor.handle_finish_vertex(u) 75 end 76 end