[SOLUTION] Pinewood Derby


#1

#!/usr/bin/env ruby

Pinewood Derby scheduling program.

class Scheduler

def initialize(car_count, lane_count, round_target)
# Set up instance variables for basic data
@cars = (1…car_count).inject([]) { |a,n| a << n }
@lanes = (1…lane_count).inject([]) { |a,n| a << n }
heat_count = round_target * car_count
@heats = (1…heat_count).inject([]) { |a,n| a << n }

# Prepare to track car in lane for heat (SELECTION RESULTS)
@heat_lane_cars = {}
@heats.each do |heat|
  @heat_lane_cars[heat] = {}
  @lanes.each do |lane|
    @heat_lane_cars[heat][lane] = nil
  end
end

# Prepare to track how many runs each car made in each lane 

(SELECTION CRITERIA)
@lane_car_runs = {}
@lanes.each do |lane|
@lane_car_runs[lane] = {}
@cars.each do |car|
@lane_car_runs[lane][car] = 0
end
end

# Prepare to track how many runs each car made against each other 

car (SELECTION CRITERIA)
@car_opponent_runs = {}
@cars.each do |car|
@car_opponent_runs[car] = {}
@cars.each do |opponent|
next if opponent == car
@car_opponent_runs[car][opponent] = 0
end
end

# Prepare to track a car's last heat (SELECTION CRITERIA)
@car_last_heats = {}
@cars.each do |car|
  @car_last_heats[car] = 0
end

end

Assign cars to lanes in heats, populating @heat_lane_cars;

also update selection criteria

def assign
@heats.each do |heat|
@lanes.each do |lane|
opponents = @heat_lane_cars[heat].values.delete_if { |car| car
== nil }
@heat_lane_cars[heat][lane] = choose_car(lane, opponents)
increment_lane_car_heats(lane, @heat_lane_cars[heat][lane])
update_car_last_heats(@heat_lane_cars[heat][lane], heat)
end
increment_car_opponent_heats(@heat_lane_cars[heat].values)
end
end

Assign a car to a lane based on selection criteria

def choose_car(lane, opponents)
# Narrow list of candidates to cars which have used this lane least
often
candidate_array = @lane_car_runs[lane].sort { |a,b| a[1] <=> b[1] }
low_count = nil
candidates = []
candidate_array.each do |candidate|
low_count ||= candidate[1]
break if candidate[1] > low_count
candidates << candidate[0]
end
# Exclude cars already in this heat
candidates -= opponents
# Weight remaining candidates based on past heats with opponents in
this heat
candidate_weights = {}
candidates.each do |candidate|
candidate_weights[candidate] = 0
opponents.each do |opponent|
candidate_weights[candidate] +=
@car_opponent_runs[candidate][opponent]
end
end
# Narrow list of candidates to cars with the lowest weight
candidate_array = candidate_weights.sort { |a,b| a[1] <=> b[1] }
low_weight = nil
candidates = []
candidate_array.each do |candidate|
low_weight ||= candidate[1]
break if candidate[1] > low_weight
candidates << candidate[0]
end
# Break tie based on which car ran least recently
least_recent_heat = @heats.length
least_recent_candidate = nil
candidates.each do |candidate|
if @car_last_heats[candidate] < least_recent_heat
least_recent_heat = @car_last_heats[candidate]
least_recent_candidate = candidate
end
end
return least_recent_candidate
end

Update @lane_car_runs selection criteria based on a car assignment

def increment_lane_car_heats(lane, car)
@lane_car_runs[lane][car] += 1
end

Update @car_last_heats selection criteria based on a car assignment

def update_car_last_heats(car, heat)
@car_last_heats[car] = heat
end

Update @car_opponent_runs selection criteria based on lane

assignments for a heat
def increment_car_opponent_heats(opponents)
opponents.each do |car|
opponents.each do |opponent|
next if car == opponent
@car_opponent_runs[car][opponent] += 1
end
end
end

Print the results of scheduling

def report
# Header lines
line = "Heat "
@lanes.sort.each do |lane|
line << "Lane #{lane} "
end
puts line
line = "---- "
@lanes.sort.each do |lane|
line << “------ "
end
puts line
# Report lines
@heats.each do |heat|
line = sprintf(”%3d “, heat)
@heat_lane_cars[heat].keys.sort.each do |lane|
line << sprintf(”%5d ", @heat_lane_cars[heat][lane])
end
puts line
end
end

end

####################

unless ARGV.length == 3
puts “Usage: #{$0} <car_count> <lane_count> <round_count>”
exit
end
s = Scheduler.new(ARGV.shift.to_i, ARGV.shift.to_i, ARGV.shift.to_i)
s.assign
s.report


#2

Kenneth C. wrote:

#!/usr/bin/env ruby

Pinewood Derby scheduling program.

class Scheduler

Sorry, Kenneth, I sent the summary to James before your solution hit, so
I didn’t include it. It’s much faster than mine and generates excellent
results! Good job! I’d like to test whether it creates “Perfect-N”
charts where possible (just curious)