Code golf: combining multiple sorted lists into a single sorted list

Question

Implement an algorithm to merge an arbitrary number of sorted lists into one sorted list. The aim is to create the smallest working programme, in whatever language you like.

Answer 1

Python, 181 chars

---

from heapq import *
def m(l):
 r=[]
 h=[]
 for x in l:
  if x:
   heappush(h, (x[0], x[1:]))
 while h:
  e,f=heappop(h)
  r.append(e)
  if f:
   heappush(h, (f.pop(0),f))
 return r

This runs in O(NlgM) time, where N is the total number of items and M is the number of lists.