How long it takes to solve the Traveling Salesman problem by brute force

traveling_salesman_brute_force_time.rb

def factorial(n)
  (1..n).reduce(:*)
end

SECONDS_PER_STEP = 0.001

def total_seconds(n)
  factorial(n) * SECONDS_PER_STEP
end

def seconds_to_years(seconds)
  seconds / 60.0 / 60.0 / 24.0 / 365.0
end

puts "Factorial of 5 is #{factorial(5)} steps"

puts "If one step takes #{SECONDS_PER_STEP} seconds, #{factorial(5)} steps takes #{total_seconds(5)} seconds"
puts "Factorial of 22 is #{factorial(22)} steps"
puts "If one step takes #{SECONDS_PER_STEP} seconds, #{factorial(22)} steps takes #{total_seconds(22)} seconds"

puts "#{total_seconds(22)} seconds is #{seconds_to_years(total_seconds(22))} years"

Output:

Factorial of 5 is 120 steps
If one step takes 0.001 seconds, 120 steps takes 0.12 seconds
Factorial of 22 is 1124000727777607680000 steps
If one step takes 0.001 seconds, 1124000727777607680000 steps takes 1.1240007277776077e+18 seconds
1.1240007277776077e+18 seconds is 35641829267.42795 years