Advent of Code day 1 part 2

take1.rb

# The no-frills take.

words = %w[ one two three four five six seven eight nine ]
hash = words.flat_map.with_index(1) { |word, index| [ [ word, index ], [ index.to_s, index ] ] }.to_h

puts DATA.readlines.sum { |line|
  _, first_digit = hash.min_by { |string, _| line.index(string) || 999 }
  _, last_digit = hash.max_by { |string, _| line.rindex(string) || -1 }

  first_digit * 10 + last_digit
}

__END__
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take2.rb

# The regex take.

words = %w[ one two three four five six seven eight nine ]
hash = words.map.with_index(1).to_h { [ _1, _2.to_s ] }
re = /(?=(#{Regexp.union(words)}|\d))/

puts DATA.readlines.sum { |line|
  digits = line.scan(re).flatten.map { hash.fetch(_1, _1) }
  (digits.first + digits.last).to_i
}

__END__
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take3.rb

# The "unkilled darlings" take.
# I love `succ` and that $var interpolation doesn't require curlies, but rarely indulge.

words = %w[ one two three four five six seven eight nine ]

puts DATA.readlines.sum { |line|
  words.each { line.gsub!(_1) { "#$&#{words.index($&).succ}#$&" } }
  line.scan(/\d/).then { _1[0] + _1[-1] }.then(&:to_i)
}

__END__
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take4.rb

# The "what if `scan` could find the first and last digit" take.

words = %w[ one two three four five six seven eight nine ]

puts DATA.readlines.sum { |line|
  words.each { line.gsub!(_1) { "#$&#{words.index($&).succ}#$&" } }
  line.scan(/(?=(\d)).*(\d)/).join.to_i
}

__END__
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take5.rb

# The one without `readlines`.

words = %w[ one two three four five six seven eight nine ]
data = DATA.read
words.each { data.gsub!(_1) { "#$&#{words.index($&).succ}#$&" } }
puts data.scan(/(?=(\d)).*(\d)/).sum { _1.join.to_i }

__END__
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