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>> As for examples of my work... it strikes me that I've almost never
>> produced a "finished" program in my life.
>
> I don't know anyone who ever thought their program was finished. Even
> games that go out the door aren't "finished" as far as the people
> working on them are concerned.
Well yeah, but you don't ship a game while it's still not playable
without a C compiler and some heavy-duty programming skills. :-P
>> And then there's the minor detail that although I know a lot of stuff
>> about stuff... how many people actually need to know what a Huffman
>> tree is? None. Nobody needs to know this.
>
> Actually, the cool places do. Read some of the google whitepapers and
> actually look at the algorithms they use. It's the first place in 25
> years I've seen using Bloom filters.
Yeah, but I won't be working for Google, will I? :-P
>> You can't do that without a postal address. (And stamps. Do you have
>> any idea how hard it is to purchase stamps?!)
>
> Now you're just making up excuses. :-) I'll admit stamp purchasing is
> unobvious in Europe to someone from America who would expect to be able
> to buy stamps at, say, the post office, but it can't be *that* difficult.
The Post Office?
Oh, you mean that place that shuts 20 minutes before I got home? :-P
[What annoys me is that there used to be a machine outside that
despenses stamps. But then they turned it off... It's still there, it
just won't give you any stamps!]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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>> Plus, all their software development stuff clearly says all over it
>> "prior experience of developing large-scale applications is an
>> absolute requirement". So I guess I fail, right there.
>
> Yoda would think otherwise. You can only fail if you don't try.
>
> Well, that's not quite true. But believe me, you won't get past the
> phone interview if they're actually serious about that.
They're talking about people who have experience with Linux kernel
development and stuff - *I* can't even *read* C.
>> Hmm. Tell me something - all that stuff I just posted? Does it make
>> any semblance of comprehensible sense?
>
> Quite! That's what people are trying to tell you. You explain things
> very clearly.
Well, *I* like to think I explain things very clearly. But unless other
people actually agree with me, I have to wonder whether I'm just kidding
myself...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> The Post Office?
>
> Oh, you mean that place that shuts 20 minutes before I got home? :-P
>
> [What annoys me is that there used to be a machine outside that despenses
> stamps. But then they turned it off... It's still there, it just won't
> give you any stamps!]
Don't you have any supermarkets or newsagents nearby? They usually open
much later and have stamps.
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>> The Post Office?
>>
>> Oh, you mean that place that shuts 20 minutes before I got home? :-P
>>
>> [What annoys me is that there used to be a machine outside that
>> despenses stamps. But then they turned it off... It's still there, it
>> just won't give you any stamps!]
>
> Don't you have any supermarkets or newsagents nearby? They usually open
> much later and have stamps.
To be honest, I've never seen stamps on sale anywhere except at a post
office. Maybe they keep 'em hidden behind the counter or something, but
I've never seen them on sale...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> To be honest, I've never seen stamps on sale anywhere except at a post
> office. Maybe they keep 'em hidden behind the counter or something, but
> I've never seen them on sale...
http://www.royalmail.com/portal/rm/jump2?catId=400046&mediaId=26800663
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>> To be honest, I've never seen stamps on sale anywhere except at a post
>> office. Maybe they keep 'em hidden behind the counter or something,
>> but I've never seen them on sale...
>
> http://www.royalmail.com/portal/rm/jump2?catId=400046&mediaId=26800663
Heh. Yeah. I ended up having to use this once...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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>> A Huffman code is a similarly straight-forward idea.
>
> Tell that to Huffman. ;-)
Huffman coding is one of those algorithms that seems delightfully
"obvious" after you've been told the algorithm. No doubt it seemed
highly non-obvious before anybody thought of it. ;-)
> Seriously, put together some essays and/or whitepapers about this stuff,
> explaining it. You might be able to get a job teaching, or find a
> publisher who will pay you to write a book. If you can write clearly
> enough to teach complex stuff like this to youngsters, you can have a
> pretty good career.
>
> If nothing else, go to your local high-school and ask them if anyone
> needs tutoring in computer programming.
Nah. Teaching requires social skills, not to mention a truly heroic
level of self-confidence. I possess neither.
I do enjoy writing about such things... but it never seems to generate
much of a reaction. I guess I'm the only person who cares. :-(
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Invisible wrote:
> [For anybody not already familiar with such things...
>
> A Min Heap is a kind of binary tree that stores data in such a way that
> retrieving the "minimum" element is an O(1) operation. Insertion and
> deletion are both O(log n), and I believe joining two heaps should be
> O(log n) as well.
data MinHeap x = Node x (MinHeap x) (MinHeap x) | Null
is_empty Null = True
is_empty _ = False
top (Null) = error "empty heap"
top (Node x _ _) = x
insert nx (Null) = Node x Null Null
insert nx (Node x h0 h1) = Node (min x nx) (insert (max x nx) h1) h0
delete (Null) = error "empty heap"
delete (Node _ h0 Null) = h0
delete (Node _ Null h1) = h1
delete (Node _ h0 h1) =
let x0 = top h0; x1 = top h1
in if x0 < x1
then Node x0 (delete h0) h1
else Node x1 (delete h1) h0
> A "heap sort" involves turning something into a heap (with O(n log n)
> complexity) and then repeatedly removing the minimum element (with O(n)
> complexity) to yield a fully sorted list.
list_to_heap = foldl' insert Null
heap_to_list = unfoldr (\h -> if is_empty h then Nothing else (top h,
delete h))
heap_sort = heap_to_list . list_to_heap
> To build a "Huffman tree", you start with a set of trivial 1-node trees.
> Each tree has a probability assigned to it. The algorithm is to simply
> select the two lowest-probability tries, remove them from the set,
> combine them into a larger tree (with a correspondingly higher
> probability) and insert this back into the set. Eventually you will have
> 1 tree with Pr=1.
data Tree x =
Leaf {prob :: Double, symbol :: x} |
Branch {prob :: Double, branch0, branch1 :: Tree x}
instance Eq (Tree x) where
x == y = prob x == prob y
instance Ord (Tree x) where
compare x y = compare (prob x) (prob y)
huffman :: (Ord x) => [(x,Double)] -> Tree x
huffman = top . build . setup
where
setup :: (Ord x) => [(x,Double)] -> MinHeap (Tree x)
setup = list_to_heap . map (\(x,pr) -> Leaf {prob = pr, symbol = x})
build :: (Ord x) => MinHeap (Tree x) -> Tree x
build (Node t Null Null) = t
build h =
let
(t0,h0) = (top h, delete h)
(t1,h1) = (top h0, delete h0)
in insert (make_branch t0 t1) h1
make_branch t0 t1 =
Branch {prob = prob t0 + prob t1, branch0 = t0, branch1 = t1}
> Here ends the lesson on algorithms and data structures.]
[You knew it had to be done...]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On Thu, 19 Jun 2008 09:25:41 +0100, Invisible <voi### [at] dev null> wrote:
>
>To be honest, I've never seen stamps on sale anywhere except at a post
>office. Maybe they keep 'em hidden behind the counter or something, but
>I've never seen them on sale...
Most newsagents keep them behind the counter and sell as many as you
want, from 1 upwards.
--
Regards
Stephen
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> Most newsagents keep them behind the counter and sell as many as you
> want, from 1 upwards.
Also if you go to the cigarette/lotto counter at the front of most large
supermarkets, they have stamps.
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