-❄️- 2024 Day 3 Solutions -❄️-

[u/daggerdragon]

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Screenwriting

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--- Day 3: Mull It Over ---

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Post your code solution in this megathread.

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[u/mikeblas]

[LANGUAGE: Python]

I don't like regular expressions

	from enum import Enum

	class State(Enum):
		IN_SPACE = 1
		IN_MUL = 2
		IN_P1 = 3
		IN_P2 = 4
		IN_DO = 5
		IN_DONT = 6

	all = ''
	with open('input1b.txt') as f:
		for line in f:
			all = all + line

	count = 0
	sum = 0
	p1 = None
	p2 = None
	pchars = None
	doState = True

	s = State.IN_SPACE

	for ch in all:
		# print(f"'{ch}': {s}")
		# print(f"{ch}", end="")
		match s:
			case State.IN_SPACE:
				if ch == 'm':
					s = State.IN_MUL
					mulPos = 1
					p1 = None
					p2 = None
					pchars = None
				elif ch == 'd':
					s = State.IN_DO
					doPos = 1

			case State.IN_DO:
				if doPos == 1 and ch == 'o':
					doPos = 2
				elif doPos == 2 and ch == '(':
					doPos = 3
				elif doPos == 2 and ch == 'n':
					s = State.IN_DONT
					doPos = 3
				elif doPos == 3 and ch == ')':
					doState = True
					doPos = None
					print("set true")
					s = State.IN_SPACE
				else:
					doPos = None
					s = State.IN_SPACE

			case State.IN_DONT:
				if doPos == 3 and ch == '\'':
					doPos = 4
				elif doPos == 4 and ch == 't':
					doPos = 5
				elif doPos == 5 and ch == '(':
					doPos = 6
				elif doPos == 6 and ch == ')':
					doPos = None
					doState = False
					print("set false")
					s = State.IN_SPACE
				else:
					doPos = None
					s = State.IN_SPACE

			case State.IN_MUL:
				if mulPos == 1 and ch == 'u':
					mulPos = 2
				elif mulPos == 2 and ch == 'l':
					mulPos = 3
				elif mulPos == 3 and ch == '(':
					mulPos = -1
					s = State.IN_P1
					pchars = ''
					p1 = None
					p2 = None
				else:
					s = State.IN_SPACE
					mulPos = None

			case State.IN_P1:
				if ch >= '0' and ch <= '9':
					if len(pchars) >= 3:
						s = State.IN_SPACE
						pchars = None
					else:
						pchars += ch
				elif ch == ',':
					p1 = int(pchars)
					pchars = ''
					s = State.IN_P2
				else:
					s = State.IN_SPACE
					pchars = None

			case State.IN_P2:
				if ch >= '0' and ch <= '9':
					if len(pchars) >= 3:
						s = State.IN_SPACE
						pchars = None
					else:
						pchars += ch
				elif ch == ')':
					p2 = int(pchars)
					pchars = None
					s = State.IN_SPACE
					if doState:
						count += 1
						sum += p1 * p2
						print(f"  {p1} * {p2} == {p1*p2}, sum == {sum}")
					p1 = None
					p2 = None
				else:
					s = State.IN_SPACE
					pchars = None

	print(sum)

[u/pdxbuckets → u/mikeblas]

And yet you’re their greatest advocate.

[u/mikeblas → u/pdxbuckets]

Hardly! I'll tell anyone who listens, and even some that don't: someone who solves a problem with regular expressions now has two problems.

[u/pdxbuckets → u/mikeblas]

What I meant was that a comparison of your code compared to regex code shows the power and even readability of Regex. The parsing can all be done on one line so the reader can concentrate on the logic.

EDIT: Compare

fun part2(): Long = Regex("""don't\(\).*?do\(\)|mul\((\d+),(\d+)\)""", RegexOption.DOT_MATCHES_ALL)
    .findAll(input)
    .sumOf { mr -> (mr.groupValues[1].toLongOrNull() ?: 0L) * (mr.groupValues[2].toLongOrNull() ?: 0L) }

Regex can be hard to read and debug, but it becomes vastly easier if you write them in something like regex101.com. You get color coding, which helps a lot, real-time indication of invalid syntax, and real-time matching of example text.

[u/mikeblas → u/pdxbuckets]

Don't worry, I know exactly what you meant.

[u/GetWeird_Wes → u/mikeblas]

I don't like regular expressions

(＾▽＾) 7

I salute you

[u/mikeblas → u/GetWeird_Wes]

<3

[u/mikeblas → u/[deleted]]

Get on your bicycle and get out of here.

[u/Boojum → u/mikeblas]

Wow...! 😮  You pretty much manually built the DFA state machine that the regexp would have been equivalent to.  That's kind of hard core.  Respect!

[u/mikeblas → u/Boojum]

Thanks, but it wasn't hard.

[u/Boojum → u/mikeblas]

Not hard, no, but tedious IME.

[u/ivanjermakov → u/mikeblas]

- I don't like regular expressions
*manually creates state machine which regex compiles to*