#!/usr/bin/env ruby

class Integer
  define_method(:"||") do |v|
    to_s.concat(v.to_s).to_i
  end
end

problem = 7
input = File.readlines("#{problem}.input").map(&:strip)
#input = DATA.read.split("\n")
  .map do |line|
    solution, expression = line.split(": ")
    [
      solution.to_i,
      expression.split(" ").map { _1.strip.to_i }
    ]
  end

OPERATIONS = [:+, :*, :"||"]

def solve(equation)
  equation[1..].each_slice(2).to_a
    .reduce(equation[0]) do |acc, (operation, number)|
    acc = acc.public_send(operation, number); acc
  end
end

def possibilities(solution, numbers)
  OPERATIONS.repeated_permutation(numbers.size - 1)
    .map { numbers.zip(_1).flatten.compact }
    .any? { solve(_1) == solution  }
end

result = input
  .select { possibilities(_1.first, _1.last) }
  .map { _1.first }
  .sum

p result

__END__
190: 10 19
3267: 81 40 27
83: 17 5
156: 15 6
7290: 6 8 6 15
161011: 16 10 13
192: 17 8 14
21037: 9 7 18 13
292: 11 6 16 20