Advent of Code 2023 Day 24

— Day 24: Never Tell Me The Odds —

What’s happening with the hailstones on Snow Island?

Considering only the X and Y axes, check all pairs of hailstones’ future paths for intersections. How many of these intersections occur within the test area?

from itertools import combinations

with open('data-2023-24.txt', 'r') as f:
    inp = f.read().splitlines()

It feels like there must be a distinct mathematical thing we can do to determine each of these things quickly.

There is definitely some text preparation we need to do to get the right form for solving.

def create_hail(x): 
    """Simpler for the list comprehension to use a function"""
    pos, vel = x.split(' @ ')
    pos = list(map(int, pos.split(', ')))
    vel = list(map(int, vel.split(', ')))
    return pos, vel
  
hail = [create_hail(x) for x in inp]

mmin = 200000000000000 
mmax = 400000000000000

ii = 0

for g,h in combinations(hail, 2):
    # print(g,h)   
    ii += 1
    # are the velocities strictly parallel? 
    if g[1][0] == h[1][0] and g[1][1] == h[1][1]: 
        print(g, h)
    # is the x diverging (less than)
    if g[0][0] < h[0][0] and g[1][0] < h[1][0]:
        print(g, h)
    if ii > 100: break
    

ii

([380596900441035, 475034410013298, 238677466991589], [-141, -244, 154]) ([396760321169379, 438525413736576, 170928320978248], [-129, -150, 253])

101

Paste part two here