Some things I did for an interview once

interviews2019.rb

# require "rspec/autorun"
# require "minitest/autorun"

# You're running a pool of servers where the servers are numbered sequentially starting from 1. Over time, any given server might explode, in which case its server number is made available for reuse. When a new server is launched, it should be given the lowest available number.

# Write a function which, given the list of currently allocated server numbers, returns the number of the next server to allocate.

# For example:

# >> next_server_number([5, 3, 1])
# 2

# >> next_server_number([5, 4, 1, 2])
# 3

# >> next_server_number([3, 2, 1])
# 4

# >> next_server_number([2, 3])
# 1

# >> next_server_number([])
# 1

# Server names consist of an alphabetic host type (e.g. "apibox") concatenated with the server number, with server numbers allocated as before (so "apibox1", "apibox2", etc. are valid hostnames).

# Write a name tracking class with two operations, allocate(host_type) and deallocate(hostname). The former should reserve and return the next available hostname, while the latter should release that hostname back into the pool.

# For example:

# >> tracker = Tracker.new

# >> tracker.allocate('apibox')
# "apibox1"

# >> tracker.allocate('apibox')
# "apibox2"

# >> tracker.deallocate('apibox1')
# nil

# >> tracker.allocate('apibox')
# "apibox1"

# >> tracker.allocate('sitebox')
# "sitebox1"

def next_server_number(arry)
  (1..).find do |index|
    !arry.include? index
  end
end

class Tracker
  # {hosttype -> [number]}
  
  def initialize
    @allocated_hosttypes = {}
  end
  
  def allocate(hosttype)
    if @allocated_hosttypes.include? hosttype 
      next_number = next_server_number(@allocated_hosttypes[hosttype])
      @allocated_hosttypes[hosttype] << next_number
    else
      @allocated_hosttypes[hosttype] = [1]
      next_number = 1
    end
    "#{hosttype}#{next_number}"
  end
  
  def deallocate(hostname)
    hosttype, number = hostname.match(/([a-z]*)(\d*)/).captures
    puts @allocated_hosttypes
    if @allocated_hosttypes.include? hosttype
      puts @allocated_hosttypes[hosttype]
      @allocated_hosttypes[hosttype].delete number.to_i
    end
    puts @allocated_hosttypes
  end
end

tracker = Tracker.new
puts tracker.allocate('apibox')
puts tracker.allocate('apibox')
puts tracker.deallocate('apibox1')
puts tracker.allocate('apibox')
puts tracker.allocate('sitebox')

require "rspec/autorun"

# plate weights (in lbs) needed to reach the target weight. The array result may either represent the plate weights needed on one side of the barbell or both sides.
# 
# Weights used to reach the target weight will be in the form of the barbell and plates of specific weights.
# 
# Rules:
# - The barbell weighs 45 lbs.
# - The barbell is always needed, so the minimum valid weight is 45 lbs.
# - Plates are weighted as 45 lbs, 35 lbs, 25 lbs, 10 lbs, and 5 lbs.
# - Any number of plate weights of a given size may be used to reach the target weight; there are no limits on the number of plate weights available for use.
# - The weights must be equal on both sides of the barbell. You cannot have a 45 lbs plate on one end and only a 25 lbs plate on the other.
# - The maximum valid weight is 405 lbs. Anything above this would not fit on the barbell.
# - You must use the heaviest plates available. To represent 55 lbs on one side, you must use the plates (45 lbs + 10 lbs). Both (25 lbs + 25 lbs + 5 lbs) and (35 lbs + 10 lbs + 10 lbs) are invalid.
# - Any input that cannot be represented is considered invalid. Invalid cases may be handled by using either the nearest valid weight or no weight.
# 
# 
# Test Cases
# 
# > plate_weights(45)
# []
# 
# > plate_weights(135)
# [45]
# 
# > plate_weights(405)
# [45, 45, 45, 45]
# 
# > plate_weights(175)
# [45, 10, 10]
# 
# > plate_weights(105)
# [25, 5]
# 
# > plate_weights(355)
# [45, 45, 45, 10, 10]
# 
# > plate_weights(215)
# [45, 35, 5]

BAR_WEIGHT = 45
MAX_WEIGHT = 405

def number_of_weights_at_weight(target, weight)
  number = target / weight
  remaining = target % weight
  [number, remaining]
end

def plate_weights target_weight
  return [] if target_weight < BAR_WEIGHT
  return [] if target_weight > MAX_WEIGHT
  
  target_weight_without_bar = target_weight - BAR_WEIGHT
  one_side = target_weight_without_bar / 2
    
  output = []
  [45, 35, 25, 10, 5].reduce(one_side) do |acc, plate|
    number, remaining = number_of_weights_at_weight(acc, plate)
    output += Array.new(number) { |i| plate }
    remaining
  end
  
  output
end

RSpec.describe do
  context "has no weights" do
    it "when target under 45" do
     expect(plate_weights(44)).to eq([])
    end
    it "when target over 405" do
     expect(plate_weights(406)).to eq([])
    end
  end
  
  examples = { 
    405 => [45, 45, 45, 45],
    135 => [45],
    175 => [45, 10, 10],
    105 => [25, 5],
    355 => [45, 45, 45, 10, 10],
    215 => [45, 35, 5],
    237 => []
  }
  
  examples.each_pair do |k,v|
    it "#{k} produces #{v}" do
      expect(plate_weights(k)).to eq(v)
    end
  end
  
end