gistfile1.coffee

# to memorize the collatz sequence length for a specific number
memory = []

Number::collatz = ->
  if @ % 2 == 0
    @ / 2
  else
    3 * @ + 1

Number::collatzSequenceLength = ->
  length = 0
  next = Number(@)
  sequence = []

  # generate collatz sequence
  while not memory[next]
    sequence.push next
    length++
    if next == 1
      break
    else
      next = next.collatz()

  # memorize values
  base = memory[next] || 0
  while value = sequence.shift()
    memory[value] = length + base
    length--

  memory[@]

maxLength = 0
number = 0
for value in [1000000..1]
  continue if memory[value] > 0
  length = value.collatzSequenceLength()

  if maxLength < length
    maxLength = length
    number = value

console.log "Max length: #{maxLength}"
console.log "Number: #{number}"