Advent of Code 2020: Day 10 - Adapter Array

aoc-2020-d10.rb

require 'benchmark'

adapters = File.readlines('input.txt').map(&:to_i).sort
maximum_jolt = adapters.last + 3
adapters.push(maximum_jolt)

# Track the number of options to get to a target jolt value
# and default to 0. The first jolt value is 0, and can only
# be reached in one way.
options = Hash.new(0)
options[0] = 1

=begin
# For the example input, here is what is being calculated:

target:  options                   => total options
     1:  only 1 option (0 + 1)     => 1
     4:  only 1 option (1 + 3)     => 1
     5:  only 1 option (4 + 1)     => 1
     6:  either 4 + 2 or 5 + 1     => 2
     7:  6 + 1 or 5 + 2 or 4 + 3   => 2 (6) + 1 (5) + 1 (4)
    10:  only 1 option (7 + 3)     => 4
    11:  only 1 option (10 + 1)    => 4
    12:  either 10 + 2 or 11 + 1   => 4 (10) + 4 (11)
    15:  only 1 option 12 + 3      => 8
    16:  only 1 option 15 + 1      => 8
    19:  only 1 option 16 + 3      => 8
    22:  only 1 option 19 + 3      => 8
=end

Benchmark.bmbm do |x|
  x.report(:part_1) do
    jolt_groups = adapters
      .each_with_index
      .map do |adapter, index|
        adapter - (index > 0 ? adapters[index - 1] : 0)
      end
      .group_by(&:itself)

    puts jolt_groups[1].length * jolt_groups[3].length
  end

  x.report(:part_2) do
    adapters.each do |target_jolts|
      options[target_jolts] = [1, 2, 3]
        .sum { |difference| options[target_jolts - difference] }
    end

    puts options[maximum_jolt]
  end
end

example.txt

1
4
5
6
7
10
11
12
15
16
19

example2.txt

28
33
18
42
31
14
46
20
48
47
24
23
49
45
19
38
39
11
1
32
25
35
8
17
7
9
4
2
34
10
3

input.txt

35
111
135
32
150
5
106
154
41
7
27
117
109
63
64
21
138
98
40
71
144
13
66
48
12
55
119
103
54
78
65
112
39
128
53
140
77
34
28
81
151
125
85
124
2
99
131
59
60
6
94
33
42
93
14
141
92
38
104
9
29
100
52
19
147
49
74
70
84
113
120
91
97
17
45
139
90
116
149
129
87
69
20
24
148
18
58
123
76
118
130
132
75
110
105
1
8
86