Created
November 15, 2009 10:37
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class Graph | |
require 'set' | |
INFINITY = 1 << 64 | |
# Constructor | |
def initialize | |
@graph = magic_hash | |
# The graph // {node => { edge1 => weight, edge2 => weight}, node2 => ... | |
@nodes = Set.new | |
end | |
def add_edge source, destination, weight | |
@graph[source][destination] = weight | |
# Begin code for non directed graph (inserts the other edge too) | |
@graph[destination][source] = weight | |
# End code for non directed graph (ie. deleteme if you want it directed) | |
@nodes << source | |
@nodes << destination | |
end | |
def dijkstra source | |
@distance = {} | |
@previous = {} | |
@nodes.each do |i| | |
@distance[i] = INFINITY | |
@previous[i] = -1 | |
end | |
@distance[source] = 0 | |
unsolved_vertices = @nodes.delete_if { |x| x.nil? } | |
while (unsolved_vertices.size > 0) | |
current_node = nil; | |
unsolved_vertices.each do |min| | |
if (not current_node) or (@distance[min] and @distance[min] < @distance[current_node]) | |
current_node = min | |
end | |
end | |
if (@distance[current_node] == INFINITY) | |
break | |
end | |
unsolved_vertices = unsolved_vertices.delete current_node | |
@graph[current_node].keys.each do |v| | |
alternative_distance = @distance[current_node] + @graph[current_node][v] | |
if (alternative_distance < @distance[v]) | |
@distance[v] = alternative_distance | |
@previous[v] = current_node | |
end | |
end | |
end | |
end | |
# To print the full shortest route to a node | |
def print_path(dest) | |
if @previous[dest] != -1 | |
print_path @previous[dest] | |
end | |
print ">#{dest}" | |
end | |
def redundant_nodes_for source, destination | |
path = [destination] | |
current = destination | |
arcs = Set.new | |
while ![-1, source].include? current | |
path << @previous[current] | |
current = @previous[current] | |
end | |
@graph.keys.each do |node| | |
@graph[node].each do |dest, weight| | |
next if adjacent_in_path? path, node, dest | |
arc = Set.new | |
arc << node << dest | |
next if arcs.include? arc | |
puts "#{node} -> #{dest} : #{weight}" | |
arcs << arc | |
end | |
end | |
end | |
private | |
def adjacent_in_path? path, source, destination | |
node = path.find_index { |x| x == source } | |
dest = path.find_index { |x| x == destination } | |
return false if node.nil? || | |
dest.nil? || | |
(node.succ != dest && | |
dest.succ != node) | |
return true | |
end | |
def magic_hash | |
Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)} | |
end | |
end | |
a = Graph.new | |
[ | |
" A, B, 50", | |
" A, D, 150", | |
" B, C, 250", | |
" B, E, 250", | |
" C, E, 350", | |
" C, D, 50", | |
" C, F, 100", | |
" D, F, 400", | |
" E, G, 200", | |
" F, G, 100", | |
].each do |array| | |
array = array.split(',') | |
array.map! { |x| x.strip } | |
source = array[0].strip | |
destination = array[1].strip | |
resistance = array[2].to_i | |
a.add_edge source, destination, resistance | |
end | |
a.dijkstra 'A' | |
puts | |
a.redundant_nodes_for 'A', 'G' |
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