ruby_quiz_119_spec.rb

class Equation

  def initialize(*args)
    @argset = args
  end

  attr_reader :argset

  def sum
    if @argset.length == 1
      return @argset.first
    else
      first  =  Equation.new(*@argset[0..-3]).sum
      operator = @argset[-2]
      second = @argset[-1]
      first.send(operator, second)
    end
  end

  def to_s
    @argset.map(&:to_s).join(" ") + " = #{sum}"
  end

  include Comparable
  def <=> (o)
    @argset <=> o.argset
  end
end


class Solver
  attr_reader :numbers
  def initialize(*numbers)
    @numbers = numbers
  end

  def solve
    possible_numbers.each do |numbers|
      inject_operators(numbers, [:+, :-, :-]).each do |equation|
        yield equation
      end
    end
  end

  def possible_numbers
    s = numbers.join("")
    s = s.insert(1, "|").insert(3,"|").insert(5, "|")
    rotate_pipes(s).map {|m| m.split("|").map(&:to_i)}.uniq
  end

  def inject_operators(numbers, operators)
    operators.permutation.to_a.uniq.map do |operator_set|
      Equation.new *(numbers.zip(operator_set).flatten.compact)
    end
  end

private
  def rotate_pipes(s)
    s.scan(/\|\d\d+/).map {|m| s.sub(m, m[0, 2].reverse.to_s + m[2..-1].to_s)}.
      map {|r| rotate_pipes(r)}.flatten + [s]
  end
end

describe "Quiz 119" do
  it "knows when the answer is 100" do
    expect(Equation.new(25, :+, 25, :+, 56, :-, 6).sum).to eql 100
  end
  it "can tell the answer to an equation" do
    expect(Equation.new(10, :+, 20).sum).to eq(30)
    expect(Equation.new(1, :+, 2, :-, 3, :-, 456789).sum).to eq(-456789)
    expect(Equation.new(1, :+, 23, :-, 4567, :-, 89).sum).to eq(-4632)
  end
  it "can return all possible equations for a set of numbers" do
    equations = Solver.new(1).inject_operators([1, 2, 3, 4], [:-, :-, :+])
    expect(equations.count).to eql 3
    expect(equations).to include Equation.new(1, :-, 2, :-, 3, :+, 4)
  end
  describe "returns all possible sets of 4 numbers for a given sent of digits" do
    it "splits 1, 2, 3, 4 into one result" do
      expect(Solver.new(1, 2, 3, 4).possible_numbers).to eql [[1, 2, 3, 4]]
    end

    it "splits 1, 2, 3, 4, 5 into 4 results" do
      expect(Solver.new(1, 2, 3, 4, 5).possible_numbers.count).to eql 4
    end

    it "splits 1, 2, 3, 4, 5, 6 into 9 results" do
      expect(Solver.new(1, 2, 3, 4, 5, 6).possible_numbers.count).to eql 10
    end

    it "splits 1, 2, 3, 4, 5, 6, 7, 8, 9 into 36 results" do
      expect(Solver.new(1, 2, 3, 4, 5, 6, 7, 8, 9).possible_numbers.count).to eql 56
    end

  end
end

Solver.new(1, 2, 3, 4, 5, 6, 7, 8, 9).solve do |equation|
  if equation.sum == 100
    puts "******************************************"
    puts equation
    puts "******************************************"
  else
    puts equation
  end
end