Description
^(?=(\d)+).+.
"Our computers are having issues, so I have no idea if we have any Chief Historians in stock! You're welcome to check the warehouse, though," says the mildly flustered shopkeeper at the North Pole Toboggan Rental Shop. The Historians head out to take a look.
The shopkeeper turns to you. "Any chance you can see why our computers are having issues again?"
The computer appears to be trying to run a program, but its memory (your puzzle input) is corrupted. All of the instructions have been jumbled up!
It seems like the goal of the program is just to multiply some numbers. It does that with instructions like mul(X,Y), where X and Y are each 1-3 digit numbers. For instance, mul(44,46) multiplies 44 by 46 to get a result of 2024. Similarly, mul(123,4) would multiply 123 by 4.
However, because the program's memory has been corrupted, there are also many invalid characters that should be ignored, even if they look like part of a mul instruction. Sequences like mul(4*, mul(6,9!, ?(12,34), or mul ( 2 , 4 ) do nothing.
For example, consider the following section of corrupted memory:
x*mul(2,4)*%&mul[3,7]!@^do_not_*mul(5,5)*+mul(32,64]then(*mul(11,8)mul(8,5)*)
Only the four highlighted sections are real mul instructions. Adding up the result of each instruction produces *161* (2*4 + 5*5 + 11*8 + 8*5).
Scan the corrupted memory for uncorrupted mul instructions. What do you get if you add up all of the results of the multiplications?
--- Part Two ---
As you scan through the corrupted memory, you notice that some of the conditional statements are also still intact. If you handle some of the uncorrupted conditional statements in the program, you might be able to get an even more accurate result.
There are two new instructions you'll need to handle:
- The
do()instruction enables futuremulinstructions. - The
don't()instruction disables futuremulinstructions.
Only the most recent do() or don't() instruction applies. At the beginning of the program, mul instructions are enabled.
For example:
x*mul(2,4)*&mul[3,7]!^*don't()*_mul(5,5)+mul(32,64](mul(11,8)un*do()*?*mul(8,5)*)
This corrupted memory is similar to the example from before, but this time the mul(5,5) and mul(11,8) instructions are disabled because there is a don't() instruction before them. The other mul instructions function normally, including the one at the end that gets re-enabled by a do() instruction.
This time, the sum of the results is *48* (2*4 + 8*5).
Handle the new instructions; what do you get if you add up all of the results of just the enabled multiplications?
Notes
- Part I: Initial thought: ugh, parsing
- OK, we need a regex to carve out the valid
mult()operations, so let's make that - Had a dumb mistake for Part I where I was replacing the
multsarray instead of pushing new elements
- OK, we need a regex to carve out the valid
- Part II: even more complicated regex.
- I'm bad but I used ChatGPT to figure this regex out, because ugh
- Even with the correct regex, I was still getting numbers that were either too high or too low
- Desperate times call for desperate measures: I went through the input, line by line, removing
don't()[chars-until-next-do()]from the string, and it still didn't work - A friend offered a different regex, but still didn't work
- Finally, the same friend clued me in on my WRONG assumption that each line in the input should start with an implicit
do(), when the correct rule is only the FIRST line does that - I ended up concatenating all input lines into one long string, running my original regex, and got the right answer!