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# Ruby Programming Challenge For Newbies | |
# RPCFN: Short Circuit (#3) | |
# By Gautam Rege | |
# Solution by Valério Farias | |
# | |
# To find the smallest path I used the dijkstra algorithm. | |
# My inspiration was this example: http://snippets.dzone.com/posts/show/7331 | |
# To execute the class first load the file: | |
# require 'short-circuit' | |
# Then initialize the class: | |
# gr = 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]]) | |
# Finally use the method solve putting the source and the target values in the parameters: | |
# gr.solve('a','g') | |
# This must return the solution: | |
# => [["a", "b", 50], ["b", "c", 250], ["b", "e", 250], ["c", "e", 350], ["d", "f", 400], ["e", "g", 200]] | |
class Graph | |
attr_reader :list, :solution | |
def initialize(graph) | |
@graph = {} | |
@nodes = Array.new | |
@INFINITY = 1 << 32 | |
@list = graph | |
graph.each do |item| | |
source = item[0] | |
target = item[1] | |
weight = item[2] | |
if @graph.has_key?(source) | |
@graph[source][target] = weight | |
else | |
@graph[source] = {target => weight} | |
end | |
if @graph.has_key?(target) | |
@graph[target][source] = weight | |
else | |
@graph[target] = {source => weight} | |
end | |
@nodes << source unless @nodes.include?(source) | |
@nodes << target unless @nodes.include?(target) | |
end | |
end | |
# based of wikipedia's pseudocode: http://en.wikipedia.org/wiki/Dijkstra's_algorithm | |
def dijkstra(s) | |
@distance = {} | |
@prev = {} | |
@nodes.each do |i| | |
@distance[i] = @INFINITY | |
@prev[i] = -1 | |
end | |
@distance[s] = 0 | |
node_list = @nodes.compact | |
while (not node_list.empty?) | |
smallest = nil; | |
node_list.each do |min| | |
if (not smallest) or (@distance[min] and @distance[min] < @distance[smallest]) | |
smallest = min | |
end | |
end | |
break if @distance[smallest] == @INFINITY | |
node_list = node_list - [smallest] | |
@graph[smallest].keys.each do |v| | |
alt = @distance[smallest] + @graph[smallest][v] | |
if (alt < @distance[v]) | |
@distance[v] = alt | |
@prev[v] = smallest | |
end | |
end | |
end | |
end | |
def solve(s,t) | |
smallest_path = [] | |
@solution = @list | |
dijkstra(s) | |
while(@prev[t]!= -1) | |
smallest_path << [@prev[t], t, @graph[t][@prev[t]]] | |
smallest_path << [t, @prev[t], @graph[t][@prev[t]]] | |
t = @prev[t] | |
end | |
# solution == list - smallest_path | |
smallest_path.each{ |i| @solution = @solution - [i] } | |
return @solution | |
end | |
end | |
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