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[REBOL] Re: More on expressions

From: carl:cybercraft at: 5-Feb-2003 21:51

On 03-Feb-03, Joel Neely wrote:
> Many thanks to all who've participated in this thread. Anyone who > wants to keep playing, skip reading this email until you've had > your fun!
Okay, I'm late to this, although I didn't skip the following, but just skimmed it to the end to see Joel's solution. ;-) And, for anyone still playing I'll leave a few lines in saying nothing so you won't see Joel's solution, or mine. So...
> For those who'd like a hint about another approach, > keep > reading > this > email > below. > . > . > . > . > . > . > . > . > . > .
> and then we recall that we only wanted the median, which means we > only wanted the ultimate value for B, giving us our final answer: > (a min b) max ((a max b) min c)
Which was wrong as it happens, but here's Joel's corrected (in a later post) version, written as a function: median3: func [a b c] [max (min a b) (min (max a b) c)] As I said, I just skimmed Joel's post that explained how he arrived at his solution, but I did notice the use of min and max. So now for a brief explaination of how I arrived at my soloution. Firstly, I worked out what I considered the easiest way to get the maximum and minimum values from A, B and C...
>> a: 1 b: 2 c: 3
== 3
>> max max a b c
== 3
>> min min a b c
== 1 This gave me the idea for my first solution...
>> difference reduce [a b c] reduce [max max a b c min min a b c]
== [2] which returned the correct result, but in a block, and difference may be against the spirit of the game anyway, since sort and so on was out. (Difference is the word I thought of first when I read Joel's original post containing his challenge.) After more doodling, I hit on the thought that this... min a b min b c min a c would produce three values, none of which would be the maximum value of A, B and C, but which would include the median value, which of course would be the maximum value of these three new values. So, put a max and a max in front of those and my solution is...
>> max max min a b min b c min a c
== 2 A triffle longer than Joel's, but very REBOL I think. (And I do so hate parens;) -- Carl Read