1require "spec_helper"
 2
 3describe "problem eight" do
 4  #The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
 5
 6  let(:data) do
 7    <<-BLAH
 8    73167176531330624919225119674426574742355349194934
 9    96983520312774506326239578318016984801869478851843
10    85861560789112949495459501737958331952853208805511
11    12540698747158523863050715693290963295227443043557
12    66896648950445244523161731856403098711121722383113
13    62229893423380308135336276614282806444486645238749
14    30358907296290491560440772390713810515859307960866
15    70172427121883998797908792274921901699720888093776
16    65727333001053367881220235421809751254540594752243
17    52584907711670556013604839586446706324415722155397
18    53697817977846174064955149290862569321978468622482
19    83972241375657056057490261407972968652414535100474
20    82166370484403199890008895243450658541227588666881
21    16427171479924442928230863465674813919123162824586
22    17866458359124566529476545682848912883142607690042
23    24219022671055626321111109370544217506941658960408
24    07198403850962455444362981230987879927244284909188
25    84580156166097919133875499200524063689912560717606
26    05886116467109405077541002256983155200055935729725
27    71636269561882670428252483600823257530420752963450
28    BLAH
29  end
30
31  #Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
32  class MassScan
33    attr_accessor :data
34
35    def initialize(data)
36      @data = data.gsub(/ /, '').gsub(/\n/, '')
37      @position = 0
38    end
39
40    def scan(digits: 4)
41      queue = []
42      max = 0
43
44      until @position > @data.size
45        fill(queue, digits)
46        result = product(queue)
47        if result > max
48          max_queue = queue.dup
49          max = result
50          puts [max, max_queue].inspect
51        end
52      end
53
54      max
55    end
56
57    private
58
59    def fill(queue, size)
60      available_room = size - queue.size
61      if available_room == 0
62        queue.shift
63        available_room = 1
64      end
65      available_room.times do |n|
66        queue.push(data[@position])
67        @position = @position + 1
68      end
69    end
70
71    def product(queue)
72      queue.inject(1) do |memo, n|
73        memo *= n.to_i
74      end
75    end
76  end
77
78  subject { MassScan.new(data) }
79
80  it "returns the four digits that produce the greatest product" do
81    expect(subject.scan(digits: 4)).to eql(5832)
82  end
83
84  it "returns the thirteen digits that produce the greatest product" do
85    expect(subject.scan(digits: 13)).to eql(23514624000)
86  end
87end