Created
March 27, 2017 05:06
-
-
Save dorkrawk/adc4b32a180bbece390c53c3a1f6636d to your computer and use it in GitHub Desktop.
Dijkstra's Algorithm implemented in Crystal
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
class Node | |
getter name, edges | |
def initialize(@name : String) | |
@edges = {} of Node => Float64 | |
end | |
def add_edge(node, weight) | |
@edges[node] = weight | |
end | |
def ==(other : Node) | |
name == other.name | |
end | |
def !=(other : Node) | |
name != other.name | |
end | |
end | |
def dijkstras_path(start : Node, goal : Node) | |
closed_set = [] of Node | |
open_set = [start] | |
came_from = {} of Node => Node | |
g_score = {} of Node => Float64 | |
g_score[start] = 0.0 | |
f_score = {} of Node => Float64 | |
f_score[start] = 0.0 | |
while !open_set.empty? | |
current = open_set.min_by { |n| f_score.fetch(n, Float64::INFINITY) } | |
return reconstruct_path(came_from, current) if current == goal | |
open_set.delete(current) | |
closed_set << current | |
current.edges.keys.each do |neighbor| | |
next if closed_set.includes?(neighbor) | |
tentative_g_score = g_score.fetch(current, Float64::INFINITY) + current.edges[neighbor] | |
if !open_set.includes?(neighbor) | |
open_set << neighbor | |
elsif tentative_g_score >= g_score.fetch(neighbor, Float64::INFINITY) | |
next | |
end | |
came_from[neighbor] = current | |
g_score[neighbor] = tentative_g_score | |
f_score[neighbor] = g_score.fetch(neighbor, Float64::INFINITY) | |
end | |
end | |
raise Exception.new("Failed to find path") | |
end | |
def reconstruct_path(came_from, current) | |
total_path = [current] | |
while came_from.keys.includes?(current) | |
current = came_from[current] | |
total_path << current | |
end | |
total_path.reverse | |
end | |
####### | |
# basic usage | |
####### | |
start = Node.new("start") | |
mid1 = Node.new("mid1") | |
mid2 = Node.new("mid2") | |
goal = Node.new("goal") | |
start.add_edge(mid1, 2.0) | |
start.add_edge(mid2, 3.0) | |
mid1.add_edge(goal, 20.0) | |
mid2.add_edge(goal, 7.0) | |
path = dijkstras_path(start, goal) | |
p path.map { |n| n.name } |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment