mergesort.rb

def mergesort(list)
  return list if list.size <= 1
  mid = list.size / 2
  merge mergesort(list[0, mid]), mergesort(list[mid, list.size])
end
 
def merge(left, right)
  sorted = []
  until left.empty? or right.empty?
    if left.first <= right.first
      sorted.push left.shift
    else
      sorted.push right.shift
    end
  end
  sorted.concat(left).concat(right)
end