For the first part you can use charsub -
https://www.jsoftware.com/help/user/lib_strings.htm#charsub
'())('charsub |.'1*2+(3*4)'
(4*3)+2*1
On Fri, Dec 18, 2020 at 19:21 'Michael Day' via Programming <
programm...@jsoftware.com> wrote:
> Unlike in the K forum, the J-wires have been virtually silent on this
> year's Advent of Code...
>
> Anyway, today's problem, number 18, might interest J & APLers as part
> 1 is ALMOST
> plug-it-in to J/APL; there's just one twist, so to speak, namely we
> need to reverse an
> arithmetic expression, eg
> 1 + (2 * 3) + (4 * (5 + 6))
> needs to be evaluated as
> ((6 + 5) * 4) + (3 * 2) + 1
>
> But, even though all numbers are single-digit, just reversing the
> string doesn't work, fairly obviously:
> |.'1 + (2 * 3) + (4 * (5 + 6))'
> ))6 + 5( * 4( + )3 * 2( + 1
>
> So the brackets need swapping. The data is supplied as strings, so I
> expected to use stringreplace,
> as found in strings.ijs
>
> But:
> |. ( ')[' , '()' , '[(' ) stringreplace '1 + (2 * 3) + (4 * (5
> + 6))'
> [[6 + 5) * 4) + [3 * 2) + 1
>
> Why don't the intermediate '[' get changed to the final ')' ?
>
> The second action in stringreplace is on the left hand argument:
> _2 [\ ,(')[' , '()' , '[(' )
> )[
> ()
> [(
>
> The first column should be items of old text and the second column
> their new replacements. But the third pair seems to be ignored.
>
> I did of course get round this little difficulty, but would have preferred
> not to reinvent the wheel.
>
> NB. Part 2 is a little more challenging, as + is defined there as taking
> precedence over * .
>
> Thanks,
>
> Mike
>
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