I took pretty much the same approach as Raul (i.e. bruteforce), but
expressed it tacitly:
NB. Day 07: Crab alignment
NB. find position globally closest to all input numbers, each step being 1
fuel unit
i07=: ".}:freads'07.txt'
irg=: <./ ([+i.@>:@-~) >./ NB. integer range spanning the range of
list y
t07=: 16,1,2,0,4,2,7,1,2,14 NB. test data part a
a07=: [: (#~ (=<./)) ] +/@: |@:(-"0 1/) irg
NB. b: similar, but each sucessive step is >:i. fuel units
b07=: [: (#~ (=<./)) ] +/@:(|@:(-"0 1/) { ([: +/\ i.@>:@(>./))@]) irg
(a07;b07)i07
I hope it comes through without any interfering line-wrapping (irg, a07,
b07 should all be single line verbs).
On Tue, Dec 28, 2021, 05:46 Raul Miller <[email protected]> wrote:
> https://adventofcode.com/2021/day/7
>
> Day 7's puzzle also had a comma separated list as its data, so again
> no parsing routine was necessary:
>
> sample=: 16,1,2,0,4,2,7,1,2,14
>
> Here, you are being rescued from a whale by a bunch of crab submarines
> -- each number represents the position of a crab submarine.
>
> The puzzle is to find the one position to move them all to which
> requires the least movement. Or, in puzzle terms the least "fuel" --
> one crab changing its position by one unit costs one fuel. To solve
> the puzzle you need to report how much fuel this "least fuel" costs.
>
> My approach here was just plain brute force: checking every candidate
> position:
>
> leastfuel=:{{
> min=.<./y
> max=.>./y
> options=.min+i.1+max-min
> fuel=. +/|y-/options
> optimum=. min+(i.<./)fuel
> optimum{fuel
> }}
>
> For part 2, the fuel cost was not constant, but increased by one each
> step. 1 step is still 1 fuel, two steps is 1+2 fuel, three steps is
> 1+2+3 fuel. In other the sum was a triangular number: -:@(*>:)distance
>
> So, I threw that expression into my routine:
>
> crab=:{{
> min=.<./y
> max=.>./y
> options=.min+i.1+max-min
> fuel=. +/-:@(*>:)|y-/options
> optimum=. min+(i.<./)fuel
> optimum{fuel
> }}
>
> I am sure that there's better ways of expressing this. That said,
> plotting the fuel costs for each of the position options suggests that
> brute force was the only viable approach here. If I am wrong about
> that, I would love to hear an explanation.
>
> --
> Raul
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>
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