2024: Day 3

Setup

The original challenge

My thoughts

• I like regex, so this one should be a little more straight forward
• Seems like {re} is the package for regular expressions in python?
• The split() function was useful here for separating out the two numbers from mult(123,212)
• Need to sort out a nice auto-formatter for formatting python code in my IDE

Part 1

import re
import numpy as np

with open("input", 'r') as file:
    # Read the entire content of the file
    input = file.read()

pattern = r'mul\(\d{1,3},\d{1,3}\)'
valid = re.findall(pattern, input)

def do_mult(commands):
    total = 0
    for i in range(len(commands)):
        stripped = commands[i][4:len(commands[i])-1]
        values = np.array(stripped.split(","), dtype=float)

        total = total + np.prod(values)
    return total

do_mult(valid)

179571322.0

Part 2

pattern = r"mul\(\d{1,3},\d{1,3}\)|do\(\)|don't\(\)"
valid = re.findall(pattern, input)

For this part I could identify all the multipliers that appear between a do and and a don’t and remove them from the valid list.

Another quick and dirty approach would be to keep track if we’re in a do or a don’t state as we loop. Which is what I went for.

def do_conditional_mult(commands):
    total = 0
    state = "do"

    for i in range(len(commands)):
        if commands[i][0:3] == "mul":
            if state == "do":
                stripped = commands[i][4:len(commands[i])-1]
                values = np.array(stripped.split(","), dtype=float)
                total = total + np.prod(values)
        elif commands[i] == "do()":
            state = "do"
        elif commands[i] == "don't()":
            state = "don't"

    return total

do_conditional_mult(valid)

103811193.0