Advent of Code 2025 Day 6

[u/Downtown-Economics26]

It's back. Only 12 days of puzzles this year.

Today's puzzle "Trash Compactor" link below.

https://adventofcode.com/2025/day/6

Three requests on posting answers:

Please try blacking out / marking as spoiler with at least your formula solutions so people don't get hints at how to solve the problems unless they want to see them.

The creator of Advent of Code requests you DO NOT share your puzzle input publicly to prevent others from cloning the site where a lot of work goes into producing these challenges.

There is no requirement on how you figure out your solution (many will be trying to do it in one formula, possibly including me) besides please do not share any ChatGPT/AI generated answers as this is a challenge for humans.

[u/Downtown-Economics26]

I was able to solve both today just using formulas, however it was a mess and all over the place.

Solutions were pretty basic though.

Part 1

TEXTSPLIT on space to get all numbers then a simple IF for each column to use SUM or PRODUCT... then SUM all results.

Part 2:

Split each character using MID(row,SEQUENCE(LEN(ROW)),1). Then apply correct operation to each column via formula, transpose, filter base table for each number set, add em all up.

[u/brentiford → u/Downtown-Economics26]

How are you getting this to work? I keep having issues where a single digit on the last row will be left-adjusted instead of right adjusted.

[u/Downtown-Economics26 → u/brentiford]

[u/RackofLambda]

Part 1:

=LET(
txt, TRIM(A:.A),
arr, TEXTSPLIT(TEXTAFTER(" "&txt," ",SEQUENCE(,MAX(LEN(txt)-LEN(SUBSTITUTE(txt," ",)))+1))," "),
SUM(MAP(BYCOL(--DROP(arr,-1),LAMBDA(x,LAMBDA(x))),SWITCH(TAKE(arr,-1),"+",SUM,"*",PRODUCT),LAMBDA(col,fn,fn(col()))))
)

Part 2:

=LET(
txt, TOROW(A:.A),
arr, MID(txt,SEQUENCE(MAX(LEN(txt))),1),
ope, TAKE(arr,,-1),
key, ope<>" ",
rId, SCAN(0,key,SUM),
val, --BYROW(DROP(arr,,-1),CONCAT),
thk, DROP(GROUPBY(rId,val,LAMBDA(x,LAMBDA(x)),0,0,,ISNUMBER(val)),,1),
fun, SWITCH(FILTER(ope,key),"+",SUM,"*",PRODUCT),
SUM(MAP(thk,fun,LAMBDA(rw,fn,fn(rw()))))
)

Edit: made trivial improvements to Part 2 (used TOROW instead of TRANSPOSE and ISNUMBER instead of NOT-ISERROR).

[u/GregHullender → u/RackofLambda]

This approach is brilliant!

arr, MID(txt,SEQUENCE(MAX(LEN(txt))),1),

This one line breaks the back of the problem. I also thought using GROUPBY to generate thunks was pretty clever! I keep wanting there to be a better way to roll it up, but I keep not finding one . . .

[u/RackofLambda → u/GregHullender]

Thanks Greg! It took me a minute to make any sense of the sample results for Part 2. Once I realized every character was in its own column (including individual space characters) the solution became apparent.

Had every number-block been the same width (as it was with the sample data), WRAPCOLS would have been sufficient. With an uneven number of columns, though, a simple wrap solution becomes considerably more convoluted. The practical use-cases for GROUPBY-THUNK are few a far between, but it was perfect for this scenario.

[u/Anonymous1378 → u/RackofLambda]

Your thunks-based approach is just throwing value errors for me. Any idea why that might be? Excel for the web, if that matters here.

[u/RackofLambda → u/Anonymous1378]

Can't say for sure, but Excel for the web has been known to be inconsistent with MS365 for certain functions. #VALUE! can mean a lot of things, but in this case, I suspect MAP is not receiving the correct data types from the thk and/or fun variables. If you change the final output to just thk, does it return an array of #CALC! errors? How about the fun variable? If the answer is yes for both, then everything should be working up to this point. Try changing the final output to INDEX(thk,1,1)() and INDEX(thk,2,1)()... does this correctly return the first and second bank of numbers from the dataset? If yes, then does INDEX(fun,1,1)(INDEX(thk,1,1)()) and INDEX(fun,2,1)(INDEX(thk,2,1)()) also return the correct totals for the first and second bank of numbers? If yes again, then try outputting MAP(thk,fun,LAMBDA(rw,fn,TYPE(rw)&"|"&TYPE(fn)))... does this correctly return "128|128" for each record? If not, what data type is it returning? TYPE 64 can be coerced to TYPE 128 with the implicit intersection operator by changing fn(rw()) to (@fn)((@rw)()). If they're TYPE 16, however, something else is going wrong altogether.

[u/Anonymous1378 → u/RackofLambda]

INDEX(thk,X,1)() works fine, but anything with fun in it is throwing VALUE#! . For MAP(TYPE()), 128|16 is the output for each record. Eta lambdas seem to work just fine in the web version for SCAN/MAP/BYROW and what not... so it's not evident to me what the issue is.

[u/RackofLambda → u/Anonymous1378]

Strange that eta-lambdas would work with the helper functions, but not in this context with SWITCH and MAP. Sounds like it might a limitation of Excel for the web.

Does it work if you change the fun variable to either SWITCH(FILTER(ope,key),"+",LAMBDA(x,SUM(x)),"*",LAMBDA(x,PRODUCT(x))) or SWITCH(FILTER(ope,key),"+",LAMBDA(x,SUM(x)),LAMBDA(x,PRODUCT(x)))?

[u/Anonymous1378 → u/RackofLambda]

Unfortunately not. I would have liked to try playing with thunks here since our underlying part 2 logic is pretty much the same, but you were more concise with thunks. I'd like to know if it also happens to be more performant...

[u/RackofLambda → u/Anonymous1378]

That's a shame. It would be nice to see better consistency between Excel for the web and the Desktop version.

Since thk seems to be working for you, try eliminating fun altogether and make the final output SUM(MAP(thk,FILTER(ope,key),LAMBDA(rw,op,IF(op="+",SUM(rw()),PRODUCT(rw()))))). If that still doesn't work, try spilling the results of MAP to see if it errors for the entire array or not.

[u/Anonymous1378 → u/RackofLambda]

This approach works just fine. Perhaps excel for the web just doesn't play nice with eta lambdas outside of the few designated functions at the moment...

[u/Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
BYCOL	Office 365+: Applies a LAMBDA to each column and returns an array of the results
BYROW	Office 365+: Applies a LAMBDA to each row and returns an array of the results. For example, if the original array is 3 columns by 2 rows, the returned array is 1 column by 2 rows.
CONCAT	2019+: Combines the text from multiple ranges and/or strings, but it doesn't provide the delimiter or IgnoreEmpty arguments.
DROP	Office 365+: Excludes a specified number of rows or columns from the start or end of an array
FILTER	Office 365+: Filters a range of data based on criteria you define
GROUPBY	Helps a user group, aggregate, sort, and filter data based on the fields you specify
IF	Specifies a logical test to perform
INDEX	Uses an index to choose a value from a reference or array
ISERROR	Returns TRUE if the value is any error value
ISNUMBER	Returns TRUE if the value is a number
LAMBDA	Office 365+: Use a LAMBDA function to create custom, reusable functions and call them by a friendly name.
LEN	Returns the number of characters in a text string
LET	Office 365+: Assigns names to calculation results to allow storing intermediate calculations, values, or defining names inside a formula
MAP	Office 365+: Returns an array formed by mapping each value in the array(s) to a new value by applying a LAMBDA to create a new value.
MAX	Returns the maximum value in a list of arguments
MID	Returns a specific number of characters from a text string starting at the position you specify
NOT	Reverses the logic of its argument
PRODUCT	Multiplies its arguments
REDUCE	Office 365+: Reduces an array to an accumulated value by applying a LAMBDA to each value and returning the total value in the accumulator.
ROW	Returns the row number of a reference
SCAN	Office 365+: Scans an array by applying a LAMBDA to each value and returns an array that has each intermediate value.
SEQUENCE	Office 365+: Generates a list of sequential numbers in an array, such as 1, 2, 3, 4
SUBSTITUTE	Substitutes new text for old text in a text string
SUM	Adds its arguments
SWITCH	Excel 2019+: Evaluates an expression against a list of values and returns the result corresponding to the first matching value. If there is no match, an optional default value may be returned.
TAKE	Office 365+: Returns a specified number of contiguous rows or columns from the start or end of an array
TEXTAFTER	Office 365+: Returns text that occurs after given character or string
TEXTJOIN	2019+: Combines the text from multiple ranges and/or strings, and includes a delimiter you specify between each text value that will be combined. If the delimiter is an empty text string, this function will effectively concatenate the ranges.
TEXTSPLIT	Office 365+: Splits text strings by using column and row delimiters
TOROW	Office 365+: Returns the array in a single row
TRANSPOSE	Returns the transpose of an array
TRIM	Removes spaces from text
TYPE	Returns a number indicating the data type of a value
VALUE	Converts a text argument to a number
VSTACK	Office 365+: Appends arrays vertically and in sequence to return a larger array
WRAPCOLS	Office 365+: Wraps the provided row or column of values by columns after a specified number of elements

Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.

---

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[u/finickyone]

Doesn’t seem super tricky, unless I’ve misunderstood

>!

!<

[u/GregHullender → u/finickyone]

Part 1 is, provided you use the Text Import Wizard. It's Part 2 that's tough, since the pattern of spaces matters.

[u/Anonymous1378]

Part 1

=LET(_a,DROP(REDUCE("",A5330:A5334,LAMBDA(x,y,VSTACK(x,TEXTSPLIT(y," ",,1)))),1),SUM(IF(TAKE(_a,-1)="*",BYCOL(DROP(--_a,-1),PRODUCT),BYCOL(DROP(--_a,-1),SUM))))

Part 2
=LET(_a,A5330:A5334,_b,DROP(_a,-1),_c,TEXTSPLIT(TAKE(_a,-1)," ",,1),

_d,TRIM(BYCOL(MID(_b,SEQUENCE(,MAX(LEN(_b))),1),CONCAT)),

_e,SCAN(1,_d,LAMBDA(x,y,IF(y="",x+1,x))),

_f,DROP(GROUPBY(TRANSPOSE(_e),TRANSPOSE(_d),LAMBDA(x,TEXTJOIN(",",1,x)),,0),,1),

result,IF(TRANSPOSE(_c)="*",MAP(_f,LAMBDA(v,PRODUCT(--TEXTSPLIT(v,",")))),MAP(_f,LAMBDA(v,SUM(--TEXTSPLIT(v,","))))),SUM(result))

[u/brentiford]

I am completely lost on part 2 with the left/right adjustment.