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require "spec_helper"
describe "problem eight" do
#The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
let(:data) do
<<-BLAH
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450
BLAH
end
#Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
class MassScan
attr_accessor :data
def initialize(data)
@data = data.gsub(/ /, '').gsub(/\n/, '')
@position = 0
end
def scan(digits: 4)
queue = []
max = 0
until @position > @data.size
fill(queue, digits)
result = product(queue)
if result > max
max_queue = queue.dup
max = result
puts [max, max_queue].inspect
end
end
max
end
private
def fill(queue, size)
available_room = size - queue.size
if available_room == 0
queue.shift
available_room = 1
end
available_room.times do |n|
queue.push(data[@position])
@position = @position + 1
end
end
def product(queue)
queue.inject(1) do |memo, n|
memo *= n.to_i
end
end
end
subject { MassScan.new(data) }
it "returns the four digits that produce the greatest product" do
expect(subject.scan(digits: 4)).to eql(5832)
end
it "returns the thirteen digits that produce the greatest product" do
expect(subject.scan(digits: 13)).to eql(23514624000)
end
end
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