[Jprogramming] String replace puzzle

['Michael Day' via Programming]

Yes, I ended up indexing brackets with    I. '()' =/ y ,  assuming that 
the left & right brackets
were balanced!

Part 2 was long-winded, recursive,  but evaluated quickly, luckily.

My slowest routine for any of these posers is for part 2 of Day 15; best 
I managed was
~ 40 seconds.

Cheers,

Mike

On 18/12/2020 19:50, Joseph Novakovich wrote:
> For part 1 I used pretty much the same approach, eval by way of
> reversing (|.&.;:):
>
>     +/ {{".'('c}')'o}y['o c'=. I. 0 1=/'()'i.y=.|.&.;:y}}&> in
>
> Mine differs mostly in avoiding library definitions, amending parens
> by index. For part 2 I used ;: to calculate a depth vector for the
> tokens and then I evaluate the deepest nested subexpressions at each
> iteration reaching fixpoint.
>
> https://github.com/jitwit/aoc/blob/a/J/20/18.ijs
>
> On 12/18/20, 'Michael Day' via Programming <programming at 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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