ruby-mergesort.rb

def mergesort(ary)
  return ary if ary.count <= 1
  size = ary.count
  m = size / 2
  merge mergesort(ary[0..m-1]), mergesort(ary[m..size-1])
end

def merge(a, b)
  return a if b.count <= 0
  return b if a.count <= 0
  min = a.first > b.first ? b.shift : a.shift
  [min] + merge(a,b)
end