Created
November 29, 2010 07:44
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Implements the algorithm used by the National Resident Matching Program (NRMP) to match residency and fellowship applicants to programs.
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# Implements the algorithm used by the National Resident Matching Program | |
# (NRMP) to match residency and fellowship applicants to programs. The | |
# algorithm is described here: | |
# http://www.nrmp.org/fellow/algorithm.html | |
# and again here: | |
# http://www.nrmp.org/res_match/about_res/algorithms.html | |
# | |
# The Test class computes the example match scenario described on those pages. | |
module Match | |
class Matcher | |
attr_accessor :applicants, :programs | |
def self.run(applicants_hash, programs_hash) | |
applicants = applicants_hash.map { |name, list| Applicant.new(name, list) } | |
programs = programs_hash.map { |name, attr| Program.new(name, attr[:positions], attr[:list]) } | |
self.new(applicants, programs).run | |
end | |
def initialize(applicants, programs) | |
self.applicants = applicants | |
self.programs = {} | |
programs.each do |program| | |
self.programs[program.name] = program | |
end | |
end | |
def run | |
while remaining_applicants.any? | |
puts "Round ##{round ||= 0; round += 1} (#{remaining_applicants.map(&:name).join(', ')})" | |
remaining_applicants.each do |applicant| | |
print " #{applicant.name}: " | |
while !applicant.exhausted_programs? && !applicant.matched? | |
program = programs[applicant.next_program] | |
print "#{program.name} " | |
program.try_to_match(applicant) | |
end | |
puts "" | |
end | |
end | |
self | |
end | |
def remaining_applicants | |
applicants.reject{|applicant| applicant.matched? || applicant.exhausted_programs? } | |
end | |
def results_description | |
"\nMatch results:\n".tap do |str| | |
programs.each { |name, program| str << program.description + "\n" } | |
str << "Unmatched: #{applicants.reject(&:matched?).map(&:name).join(', ')}" | |
end | |
end | |
end | |
class Program | |
attr_accessor :name, :positions, :list, :matches | |
def initialize(name, positions, list) | |
self.name = name | |
self.positions = positions | |
self.list = list | |
self.matches = [] | |
end | |
def try_to_match(applicant) | |
if list.index(applicant.name) | |
print "(#{list.index(applicant.name)}) " | |
matches << applicant | |
applicant.matched = true | |
cull_matches | |
else | |
print "(unranked) " | |
end | |
end | |
def cull_matches | |
while matches.size > positions do | |
reject = matches.sort_by{|applicant| list.index(applicant.name) }.last | |
reject.matched = false | |
matches.delete(reject) | |
print "[culled #{reject.name}] " | |
end | |
end | |
def description | |
"#{name}: #{matches.map(&:name).join(', ')} #{"(#{positions - matches.size} unfilled)" if matches.size < positions}" | |
end | |
end | |
class Applicant | |
attr_accessor :name, :list, :matched | |
def initialize(name, list) | |
self.name = name | |
self.list = list | |
@ranking_position = -1 | |
end | |
def exhausted_programs? | |
@ranking_position >= self.list.size - 1 | |
end | |
def next_program | |
raise "No ranked programs available!" if exhausted_programs? | |
@ranking_position += 1 | |
self.list[@ranking_position] | |
end | |
def matched? | |
matched | |
end | |
end | |
end | |
class Test | |
PROGRAMS = { | |
'city' => {:positions => 2, :list => ['garcia', 'hassan', 'eastman', 'anderson', 'brown', 'chen', 'davis', 'ford']}, | |
'general' => {:positions => 2, :list => ['brown', 'eastman', 'hassan', 'anderson', 'chen', 'davis', 'garcia']}, | |
'mercy' => {:positions => 2, :list => ['chen', 'garcia']}, | |
'state' => {:positions => 2, :list => ['brown', 'eastman', 'anderson', 'chen', 'hassan', 'ford', 'davis', 'garcia']} | |
} | |
APPLICANTS = { | |
'anderson' => ['city'], | |
'brown' => ['city', 'mercy'], | |
'chen' => ['city', 'mercy'], | |
'davis' => ['mercy', 'city', 'general', 'state'], | |
'eastman' => ['city', 'mercy', 'state', 'general'], | |
'ford' => ['city', 'general', 'mercy', 'state'], | |
'garcia' => ['city', 'mercy', 'state', 'general'], | |
'hassan' => ['state', 'city', 'mercy', 'general'] | |
} | |
def self.main | |
matcher = Match::Matcher.run(APPLICANTS, PROGRAMS) | |
puts matcher.results_description | |
end | |
end | |
Test.main |
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Round #1 (chen, anderson, brown, garcia, davis, ford, eastman, hassan) | |
chen: city (5) | |
anderson: city (3) | |
brown: city (4) [culled chen] | |
garcia: city (0) [culled brown] | |
davis: mercy (unranked) city (6) [culled davis] general (5) | |
ford: city (7) [culled ford] general (unranked) mercy (unranked) state (5) | |
eastman: city (2) [culled anderson] | |
hassan: state (4) | |
Round #2 (chen, brown) | |
chen: mercy (0) | |
brown: mercy (unranked) | |
Match results: | |
city: garcia, eastman | |
mercy: chen (1 unfilled) | |
general: davis (1 unfilled) | |
state: ford, hassan | |
Unmatched: anderson, brown |
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