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    <p><strong>Python: 113 characters</strong></p> <pre><code>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: &gt;&gt;&gt; m([], [[1,4], [2,6], [3,5]]) [1, 2, 3, 4, 5, 6] </code></pre> <p><strong>EDIT:</strong> 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:</p> <ul> <li>my solution (<em>Merge</em>)</li> <li><code>sorted(sum(lists, []))</code> (<em>Built-in</em>)</li> <li><a href="https://stackoverflow.com/questions/464960/code-golf-combining-multiple-sorted-lists-into-a-single-sorted-list#465044">Deestan's solution</a> which sorted in a different way (<em>Re-implement</em>)</li> </ul> <p><img src="https://i622.photobucket.com/albums/tt302/gefafwisp/merge_gr.png" alt="List merge performance"></p> <p><strong>EDIT</strong>2: (JFS)</p> <p>The figure's labels:</p> <ul> <li><code>merge_26</code> -- <code>heapq.merge()</code> from Python 2.6 stdlib </li> <li><code>merge_alabaster</code> -- the above code (labeled <code>Merge</code> on the above figure)</li> <li><code>sort_builtin</code> -- <code>L = sum(lists,[]); L.sort()</code></li> <li><a href="https://stackoverflow.com/questions/464960/code-golf-combining-multiple-sorted-lists-into-a-single-sorted-list#465044">Deestan's solution</a> is O(N**2) so it is excluded from the comparison (all other solutions are O(N) (for the input provided))</li> </ul> <p>Input data are <code>[f(N) for _ in range(10)]</code>, where <code>f()</code> is:</p> <pre><code>max_ = 2**31-1 def f(N): L = random.sample(xrange(max_), n) L.sort() return L f.__name__ = "sorted_random_%d" % max_ </code></pre> <p><img src="https://i.stack.imgur.com/6Ngpo.png" alt="Performance data Nmax=2**16"> NOTE: <code>merge_alabaster()</code> doesn't work for <code>N &gt; 100</code> due to <code>RuntimeError: "maximum recursion depth exceeded"</code>.</p> <p>To get <a href="http://gist.github.com/51074" rel="nofollow noreferrer">Python scripts that generated this figure</a>, type:</p> <pre><code>$ git clone git://gist.github.com/51074.git </code></pre> <p>Conclusion: For reasonably large lists the built-in sort shows near linear behaviour and it is the fastest. </p>
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    1. POCode golf: combining multiple sorted lists into a single sorted list
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    1. COTest you function for `[[1]*10 for _ in range(100)]` input (expected output `[1]*1000`). I've tested `L = sum(lists, []); L.sort()`; it is faster than version based on `heapq.merge()` (Python 2.6) for the inputs I've tried `
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    2. CO`len(m([], [[1]*10 for _ in range(100)]))` must be `1000`, but it returns `994`.
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    3. COOh cool, that's an interesting bug! In golfifying my solution, I used the `except:` which masks the "RuntimeError: maximum recursion depth exceeded in cmp" you get when l is very long. The "never use a bare except" rule wins again.
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