78 lines
3.8 KiB
Markdown
78 lines
3.8 KiB
Markdown
# 2018 Day 11: Chronal Charge
|
|
Copyright (c) Eric Wastl
|
|
#### [Direct Link](https://adventofcode.com/2018/day/11)
|
|
|
|
## Part 1
|
|
|
|
You watch the Elves and their sleigh fade into the distance as they head toward the North Pole.
|
|
|
|
Actually, you're the one fading. The falling sensation returns.
|
|
|
|
The low fuel warning light is illuminated on your wrist-mounted device. Tapping it once causes it to project a hologram of the situation: a **300x300** grid of fuel cells and their current power levels, some negative. You're not sure what negative power means in the context of time travel, but it can't be good.
|
|
|
|
Each fuel cell has a coordinate ranging from **1 to 300** in both the X (horizontal) and Y (vertical) direction. In `X,Y` notation, the top-left cell is `1,1`, and the top-right cell is `300,1`.
|
|
|
|
The interface lets you select **any 3x3 square** of fuel cells. To increase your chances of getting to your destination, you decide to choose the 3x3 square with the **largest total power**.
|
|
|
|
The power level in a given fuel cell can be found through the following process:
|
|
|
|
- Find the fuel cell's **rack ID**, which is its **X coordinate plus 10**.
|
|
- Begin with a power level of the **rack ID** times the **Y coordinate**.
|
|
- Increase the power level by the value of the **grid serial number** (your puzzle input).
|
|
- Set the power level to itself multiplied by the **rack ID**.
|
|
- Keep only the **hundreds digit** of the power level (so `12345` becomes 3; numbers with no hundreds digit become `0`).
|
|
- **Subtract 5** from the power level.
|
|
|
|
For example, to find the power level of the fuel cell at 3,5 in a grid with serial number `8`:
|
|
|
|
- The rack ID is `3 + 10 = 13`.
|
|
- The power level starts at `13 * 5 = 65`.
|
|
- Adding the serial number produces `65 + 8 = 73`.
|
|
- Multiplying by the rack ID produces `73 * 13 = 949`.
|
|
- The hundreds digit of `949` is `9`.
|
|
- Subtracting 5 produces `9 - 5 = 4`.
|
|
|
|
So, the power level of this fuel cell is **`4`**.
|
|
|
|
Here are some more example power levels:
|
|
|
|
- Fuel cell at `122, 79`, grid serial number `57`: power level `-5`.
|
|
- Fuel cell at `217,196`, grid serial number `39`: power level `0`.
|
|
- Fuel cell at `101,153`, grid serial number `71`: power level `4`.
|
|
|
|
Your goal is to find the 3x3 square which has the largest total power. The square must be entirely within the 300x300 grid. Identify this square using the `X,Y` coordinate of its **top-left fuel cell**. For example:
|
|
|
|
For grid serial number `18`, the largest total 3x3 square has a top-left corner of **`33,45`** (with a total power of `29`); these fuel cells appear in the middle of this 5x5 region:
|
|
|
|
```
|
|
-2 -4 4 4 4
|
|
-4 4 4 4 -5
|
|
4 3 3 4 -4
|
|
1 1 2 4 -3
|
|
-1 0 2 -5 -2
|
|
```
|
|
|
|
For grid serial number `42`, the largest 3x3 square's top-left is **`21,61`** (with a total power of `30`); they are in the middle of this region:
|
|
|
|
```
|
|
-3 4 2 2 2
|
|
-4 4 3 3 4
|
|
-5 3 3 4 -4
|
|
4 3 3 4 -3
|
|
3 3 3 -5 -1
|
|
```
|
|
|
|
**What is the `X,Y` coordinate of the top-left fuel cell of the 3x3 square with the largest total power?**
|
|
|
|
## Part 2
|
|
|
|
You discover a dial on the side of the device; it seems to let you select a square of **any size**, not just 3x3. Sizes from 1x1 to 300x300 are supported.
|
|
|
|
Realizing this, you now must find the **square of any size with the largest total power**. Identify this square by including its size as a third parameter after the top-left coordinate: a 9x9 square with a top-left corner of `3,5` is identified as `3,5,9`.
|
|
|
|
For example:
|
|
|
|
- For grid serial number `18`, the largest total square (with a total power of `113`) is 16x16 and has a top-left corner of `90,269`, so its identifier is **`90,269,16`**.
|
|
- For grid serial number `42`, the largest total square (with a total power of `119`) is 12x12 and has a top-left corner of `232,251`, so its identifier is **`232,251,12`**.
|
|
|
|
**What is the X,Y,size identifier of the square with the largest total power?** |