quicksort.rb

def mergesort(array)
  if array.count <= 1
    return array #Sorted!
  end

  half = array.count / 2
  a = mergesort(array.slice(0,half))
  b = mergesort(array.slice(half,array.count - half))

  array = [] #Empty it to start sortinng
  a_off = 0
  b_off = 0
  while a_off < a.count && b_off < b.count
    num_a = a[a_off]
    num_b = b[b_off]

    put_largest(array,num_a,num_b) ? a_off += 1 :  b_off += 1
    
  end

  fill_from(array,a,a_off)
  fill_from(array,b,b_off)

  return array
end

def put_largest(dest,a,b)
  if a <= b
    dest << a
    return true
  else
    dest << b
    return false
  end
end

def fill_from(dest,src,start)
  while start < src.count
    dest << src[start]
    start += 1
  end
end

puts mergesort [9,8,7,6,5,4,3,2,1]