danielcristofani · December 4, 2025 04:53
diff --git a/2025day3.b b/2025day3.b
 [2025day3.b -- 2025 Advent of Code Day 3
 (c) 2025 Daniel B. Cristofani
 http://brainfuck.org/
 This program is licensed under a Creative Commons Attribution-ShareAlike 4.0
 International License (http://creativecommons.org/licenses/by-sa/4.0/).

 This program solves Advent of Code 2025, Day 3.
 (https://adventofcode.com/2025/day/3)

 You can change battery count in parentheses at the start for part 1 or 2.

 This uses a moving window on the input text; I'm sure many people found the
 same solution. A chunk of the input text is paired with a matching array of
 "highest value found for this position"; each time we shift the input text,
 we check, from most to least significant digit, "is this better than what
 we already have"; if so, we replace that "best" value, AND all less
 significant digits' best values, with the matching input digits.

 When we find a linefeed we add the final "best" values into our running
 total and reset "best" and "input" to all 1s. They're kept nonzero to keep
 track of the length of our window. This means the program doesn't reject
 invalid banks with fewer batteries than the specified count, but I wasn't
 going to bother doing that anyway.

 Basic memory layout is:
 0 0 0 0 b 0 i t b 0 i t b 0 i t ... b 0 i t 0 0 0 ...
 where b is "best found", i is "input", t is "total". t is stored such that
 a 0 digit has a cell value of 1 and a 9 digit has a cell value of 10, so we
 can track the length of it. b and i are stored as 0=0.

 This is O(12*input length), about 0.06 seconds on my laptop. It assumes
 EOF="no change" or EOF=0. Does not assume cells are bytes, I don't think.

 If you have questions or comments, feel free to email me, and/or consider
 reading my "get good at brainfuck" series (https://brainfuck.org/ggab.html)
 which I wrote to try to help people get a handle on the language.]

 >>>>(++++++++++++)[-[>>>>+<<<<-]+>>+>+>]<[<<<<]<,[
  ----------[
    -->++++++[<------>-]>[>>>>]<<[-]<<[<<[>>>>+<<<<-]<<]>>>>[>>]<<[
      >>+<<[<<[-<<<+>>>>>-<]>]>>>[<<<+[>]]<-<<<<<<<[>>>+>>+<<<<<-]
      >>>>[->[<<[-]>>[<+>-]<[<+>>+<-]<<<]>>>]<<<
    ]<
  ]>>[
    [[>>>+<<<-]+>>[-]>>]<[<<<<]>>>>[
      <<++++++++++[>>[->>+<<<]<[>]<-]
      >>[>>[-]>>[-<<]<<[>>]>>++<<<<[>>+<<-]]>>[<<+>>-]>>
    ]>-[+<<-]+[>>+<<<<<<]>>>
  ]<,
 ]>>>>>[++>[-]++++++++>>>]<<<[+[<+++++>-]<.<<<]
	[2025day3.b -- 2025 Advent of Code Day 3
	(c) 2025 Daniel B. Cristofani
	http://brainfuck.org/
	This program is licensed under a Creative Commons Attribution-ShareAlike 4.0
	International License (http://creativecommons.org/licenses/by-sa/4.0/).

	This program solves Advent of Code 2025, Day 3.
	(https://adventofcode.com/2025/day/3)

	You can change battery count in parentheses at the start for part 1 or 2.

	This uses a moving window on the input text; I'm sure many people found the
	same solution. A chunk of the input text is paired with a matching array of
	"highest value found for this position"; each time we shift the input text,
	we check, from most to least significant digit, "is this better than what
	we already have"; if so, we replace that "best" value, AND all less
	significant digits' best values, with the matching input digits.

	When we find a linefeed we add the final "best" values into our running
	total and reset "best" and "input" to all 1s. They're kept nonzero to keep
	track of the length of our window. This means the program doesn't reject
	invalid banks with fewer batteries than the specified count, but I wasn't
	going to bother doing that anyway.

	Basic memory layout is:
	0 0 0 0 b 0 i t b 0 i t b 0 i t ... b 0 i t 0 0 0 ...
	where b is "best found", i is "input", t is "total". t is stored such that
	a 0 digit has a cell value of 1 and a 9 digit has a cell value of 10, so we
	can track the length of it. b and i are stored as 0=0.

	This is O(12*input length), about 0.06 seconds on my laptop. It assumes
	EOF="no change" or EOF=0. Does not assume cells are bytes, I don't think.

	If you have questions or comments, feel free to email me, and/or consider
	reading my "get good at brainfuck" series (https://brainfuck.org/ggab.html)
	which I wrote to try to help people get a handle on the language.]

	>>>>(++++++++++++)[-[>>>>+<<<<-]+>>+>+>]<[<<<<]<,[
	----------[
	-->++++++[<------>-]>[>>>>]<<[-]<<[<<[>>>>+<<<<-]<<]>>>>[>>]<<[
	>>+<<[<<[-<<<+>>>>>-<]>]>>>[<<<+[>]]<-<<<<<<<[>>>+>>+<<<<<-]
	>>>>[->[<<[-]>>[<+>-]<[<+>>+<-]<<<]>>>]<<<
	]<
	]>>[
	[[>>>+<<<-]+>>[-]>>]<[<<<<]>>>>[
	<<++++++++++[>>[->>+<<<]<[>]<-]
	>>[>>[-]>>[-<<]<<[>>]>>++<<<<[>>+<<-]]>>[<<+>>-]>>
	]>-[+<<-]+[>>+<<<<<<]>>>
	]<,
	]>>>>>[++>[-]++++++++>>>]<<<[+[<+++++>-]<.<<<]