Advent of Code 2025 Day 7

Author

Nathan Moore

— Day 7: Laboratories —

We have to make a teleporter work, by directing some lasers through Tachyon Manifolds.

Analyze your manifold diagram. How many times will the beam be split?

import numpy as np

with open('data-2025-07.txt', 'r') as f:
    inp = f.read().splitlines()

lists = [list(i) for i in inp]

tach = np.array(lists)

The upper bound of this is the number of splitters i.e. ^ in the input. Not all of them will be hit by lasers.

tach = np.array(lists)

summer = 0

for v in range(len(tach)): 
    for w in range(len(tach[v])): 
        if tach[v,w] == 'S': 
            # v,w
            tach[v+1,w] = '|'
        elif v == 0: 
            # we can only find S on row 0, skip this
            # there can't be any lasers and we can't test the row above
            pass
        elif tach[v,w] == '.' and tach[v-1,w] == '.': 
            # no beams, don't do anything
            pass
        elif tach[v,w] == '^' and tach[v-1,w] == '.': 
            # no beams meeting this splitter, skip
            pass
        elif tach[v,w] == '.' and tach[v-1,w] == '|': 
            # extend the beam downwards
            tach[v,w] = '|'
        elif tach[v,w] == '^' and tach[v-1,w] == '|': 
            # split the beam
            summer += 1
            tach[v,w-1] = '|'
            tach[v,w+1] = '|'
        elif tach[v,w] == '.' and tach[v-1,w] == '^': 
            # covering off possibilities, do nothing here
            pass
        elif tach[v,w] == '|' and tach[v-1,w] == '.': 
            # covering off possibilities, do nothing here
            pass
        elif tach[v,w] == '|' and tach[v-1,w] == '|': 
            # covering off possibilities, do nothing here
            pass
        else: 
            # this is just for S, | when we go through tach[1]
            print('what are the other options?')
            tach[v-1,w], tach[v,w]

summer

# 1675

what are the other options?

— Part Two —

Apply the many-worlds interpretation of quantum tachyon splitting to your manifold diagram. In total, how many different timelines would a single tachyon particle end up on?

If I do the same loop, but I don’t count instances where there is already a beam, does that get me the right answer?

Ah - instead of counting each split as one, each split is now two possible paths, but it’s not always strictly double? Could it be as simple as 2n-1? n**2? No, that’s too low.

Looking through a bunch of examples on reddit I still don’t fully get it but this one was the most helpful.

https://www.reddit.com/r/adventofcode/comments/1pg9w66/comment/nsv7z78/

There are a bunch of others in the thread of course.

curr = [0]*len(inp[0])

curr[inp[0].index('S')] = 1

p1, p2 = 0, 1
for i in inp[1:]:
    for col in range(len(curr)):
       if curr[col] > 0 and i[col] == '^':
          p1 += 1
          p2 += curr[col]
          curr[col-1] += curr[col]
          curr[col+1] += curr[col]
          curr[col] = 0

print(p1, p2)

1675 187987920774390

I also quite like this object oriented approach with classes and functions

https://github.com/RD-Dev-29/advent_of_code_25/blob/main/code_files/day7.py

This is a slightly different but common approach, create a dictionary and track the timelines.