recursive memoization with hashes

Memoization.rb

require 'benchmark'

def factorial(x)
  x == 1 ? 1 : x * factorial(x-1)
end

factorial_hash ||= Hash.new do |hash,key|
  key == 1 ? (key = 1) : (hash[key] =  key * hash[key-1])
end


def fibonacci(n)
  n <= 2 ? 1 : fibonacci(n - 1) + fibonacci(n - 2)
end


fib_hash ||= Hash.new do |hash,key|
  hash[key] = hash[key-1] + hash[key-2]
end
# initalise special cases
fib_hash[1] = 1; fib_hash[2] = 1




Benchmark.bm do |bm|
  puts "---------- factorial benchmarks -------------"
  n = 3000
  bm.report(:factorial) {  factorial(n) }
  bm.report(:factorial) {  factorial(n) }
  bm.report(:factorial_hash) {  factorial_hash[n] }
  bm.report(:factorial_hash) {  factorial_hash[n] }

  puts "---------- fibonacci benchmarks -------------"
  n = 35
  bm.report(:fibonacci) {  fibonacci(n) }
  bm.report(:fibonacci) {  fibonacci(n) }
  bm.report(:fibonacci_hash) {  fib_hash[n] }
  bm.report(:fibonacci_hash) {  fib_hash[n] }


end