# Day 7: Laboratories

[https://adventofcode.com/2025/day/7](https://adventofcode.com/2025/day/7)

## Description

### Part One

You thank the cephalopods for the help and exit the trash compactor, finding yourself in the [familiar](https://adventofcode.com/2024/day/6) [halls](https://adventofcode.com/2018/day/4) of a North Pole research wing.

Based on the large sign that says "teleporter hub", they seem to be researching _teleportation_; you can't help but try it for yourself and step onto the large yellow teleporter pad.

Suddenly, you find yourself in an unfamiliar room! The room has no doors; the only way out is the teleporter. Unfortunately, the teleporter seems to be leaking [magic smoke](https://en.wikipedia.org/wiki/Magic_smoke).

Since this is a teleporter lab, there are lots of spare parts, manuals, and diagnostic equipment lying around. After connecting one of the diagnostic tools, it helpfully displays error code `0H-N0`, which apparently means that there's an issue with one of the _tachyon manifolds_.

You quickly locate a diagram of the tachyon manifold (your puzzle input). A tachyon beam enters the manifold at the location marked `S`; tachyon beams always move _downward_. Tachyon beams pass freely through empty space (`.`). However, if a tachyon beam encounters a splitter (`^`), the beam is stopped; instead, a new tachyon beam continues from the immediate left and from the immediate right of the splitter.

For example:

    .......S.......
    ...............
    .......^.......
    ...............
    ......^.^......
    ...............
    .....^.^.^.....
    ...............
    ....^.^...^....
    ...............
    ...^.^...^.^...
    ...............
    ..^...^.....^..
    ...............
    .^.^.^.^.^...^.
    ...............
    

In this example, the incoming tachyon beam (`|`) extends downward from `S` until it reaches the first splitter:

    .......S.......
    .......|.......
    .......^.......
    ...............
    ......^.^......
    ...............
    .....^.^.^.....
    ...............
    ....^.^...^....
    ...............
    ...^.^...^.^...
    ...............
    ..^...^.....^..
    ...............
    .^.^.^.^.^...^.
    ...............
    

At that point, the original beam stops, and two new beams are emitted from the splitter:

    .......S.......
    .......|.......
    ......|^|......
    ...............
    ......^.^......
    ...............
    .....^.^.^.....
    ...............
    ....^.^...^....
    ...............
    ...^.^...^.^...
    ...............
    ..^...^.....^..
    ...............
    .^.^.^.^.^...^.
    ...............
    

Those beams continue downward until they reach more splitters:

    .......S.......
    .......|.......
    ......|^|......
    ......|.|......
    ......^.^......
    ...............
    .....^.^.^.....
    ...............
    ....^.^...^....
    ...............
    ...^.^...^.^...
    ...............
    ..^...^.....^..
    ...............
    .^.^.^.^.^...^.
    ...............
    

At this point, the two splitters create a total of only _three_ tachyon beams, since they are both dumping tachyons into the same place between them:

    .......S.......
    .......|.......
    ......|^|......
    ......|.|......
    .....|^|^|.....
    ...............
    .....^.^.^.....
    ...............
    ....^.^...^....
    ...............
    ...^.^...^.^...
    ...............
    ..^...^.....^..
    ...............
    .^.^.^.^.^...^.
    ...............
    

This process continues until all of the tachyon beams reach a splitter or exit the manifold:

    .......S.......
    .......|.......
    ......|^|......
    ......|.|......
    .....|^|^|.....
    .....|.|.|.....
    ....|^|^|^|....
    ....|.|.|.|....
    ...|^|^|||^|...
    ...|.|.|||.|...
    ..|^|^|||^|^|..
    ..|.|.|||.|.|..
    .|^|||^||.||^|.
    .|.|||.||.||.|.
    |^|^|^|^|^|||^|
    |.|.|.|.|.|||.|
    

To repair the teleporter, you first need to understand the beam-splitting properties of the tachyon manifold. In this example, a tachyon beam is split a total of _`21`_ times.

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