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: 113 characters

def m(c,l):
    try:
        c += [l[min((m[0], i) for i,m in enumerate(l) if m)[1]].pop(0)]
        return m(c,l)
    except:
        return c

# called as:
>>> m([], [[1,4], [2,6], [3,5]])
[1, 2, 3, 4, 5, 6]

EDIT: seeing as talk of performance has come up in a few places, I'll mention that I think this is pretty efficient implementation, especially as the lists grow. I ran three algorithms on 10 lists of sorted random numbers:

• my solution (Merge)
• sorted(sum(lists, [])) (Built-in)
• Deestan's solution which sorted in a different way (Re-implement)

EDIT2: (JFS)

The figure's labels:

• merge_26 -- heapq.merge() from Python 2.6 stdlib
• merge_alabaster -- the above code (labeled Merge on the above figure)
• sort_builtin -- L = sum(lists,[]); L.sort()
• Deestan's solution is O(N**2) so it is excluded from the comparison (all other solutions are O(N) (for the input provided))

Input data are [f(N) for _ in range(10)], where f() is:

max_ = 2**31-1
def f(N):
    L = random.sample(xrange(max_), n)
    L.sort()
    return L
f.__name__ = "sorted_random_%d" % max_

NOTE: merge_alabaster() doesn't work for N > 100 due to RuntimeError: "maximum recursion depth exceeded".

To get Python scripts that generated this figure, type:

$ git clone git://gist.github.com/51074.git

Conclusion: For reasonably large lists the built-in sort shows near linear behaviour and it is the fastest.