ai_advent_code_2024/lib/advent_code2024/solutions/day03

Day 3: Mull It Over

Problem Description

The North Pole Toboggan Rental Shop's computers are having issues with corrupted memory. The program is trying to multiply numbers but the instructions are jumbled up.

Rules

• Valid instructions are in the format mul(X,Y) where X and Y are 1-3 digit numbers
• Example: mul(44,46) multiplies 44 by 46 to get 2024
• Invalid instructions should be ignored, examples:
  • mul(4*
  • mul(6,9!
  • ?(12,34)
  • mul ( 2 , 4 )

Example

Given the corrupted memory:

xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))

Only these instructions are valid:

• mul(2,4)
• mul(5,5)
• mul(11,8)
• mul(8,5)

Total = (2*4) + (5*5) + (11*8) + (8*5) = 161

Task

Scan the corrupted memory for valid mul instructions and sum their results.

Part Two: Conditional Processing

The solution needs to handle two additional control instructions that affect multiplication processing:

1. do() - enables future multiplication instructions
2. don't() - disables future multiplication instructions

Key rules:

• Multiplications start enabled by default
• Only the most recent do()/don't() instruction applies
• Only enabled multiplications should be calculated and summed
• Control instructions can appear anywhere in the corrupted input

Example:

mul(2,4)don't()mul(5,5)do()mul(8,5)

Result = 48 because:

• mul(2,4) starts enabled (= 8)
• don't() disables mul(5,5) (ignored)
• do() re-enables mul(8,5) (= 40)
• Total: 8 + 40 = 48