project euler 28

euler28.rb

require 'benchmark'

def build_spiral(spiral_size)
  total = 0
  spiral_size.step(1, -2) do |i|
    v1= i**2
    i -= 1
    total += i == 0 ? 1 : [v1, v1-i, v1-2*i, v1-3*i].inject{ |sum,x| sum + x }
  end
  total
end

p build_spiral(1001)

puts Benchmark.measure {build_spiral(1001)}
=> 0.010000  0.000000  0.010000 (  0.002089)

euler28_refined.rb

require 'benchmark'
def build_spiral(spiral_size)
  return 1 if spiral_size == 1
  total = 1
  (3..spiral_size).step(2).to_a.each do |i|
    value = i**2
    i -= 1
    total += (value + (value-i) + (value-2*i) + (value-3*i))
  end
  total
end
p build_spiral(1001)
puts Benchmark.measure {build_spiral(1001)}
=> 0.000000   0.000000   0.000000 (  0.000923)