Method to order list with dependancies - ruby-on-rails

Question

Conditions: Have to use web based solution (HTML/CSS), Have to use Ruby on Rails, no use of database.
Imagine we have a list of jobs, each represented by a character. Because certain jobs must be done before others, a job may have a dependency on another job. For example, a may depend on b, meaning the final sequence of jobs should place b before a. If a has no dependency, the position of a in the final sequence does not matter. These jobs would be input with a simple text box (also how does one store multiple variables)
Given the following job structure:
a =>
b =>
c =>
The result should be a sequence containing all three jobs abc in no significant order.
Given the following job structure:
a =>
b => c
c => f
d => a
e => b
f =>
The result should be a sequence that positions f before c, c before b, b before e and a before d containing all six jobs abcdef.
Given the following job structure:
a =>
b => c
c => f
d => a
e =>
f => b
The result should be an error stating that jobs can’t have circular dependencies.

Answer 1

This should work:
module JobDependenciesResolver
def self.organize(dependencies)
unresolved_dependencies = dependencies.dup
sorted_jobs = []
until unresolved_dependencies.empty? do
doable_jobs = get_doable_jobs unresolved_dependencies, sorted_jobs
raise Exception.new("Not able to resolve dependencies") if doable_jobs.empty?
sorted_jobs += doable_jobs
unresolved_dependencies.delete_if {|key,value| sorted_jobs.include? key}
end
sorted_jobs
end
private
def self.get_doable_jobs(dependencies, job_array)
dependencies.select {|job, dependency| ([*dependency]-job_array).empty? }.keys
end
end