diff --git a/2021/09/README.md b/2021/09/README.md new file mode 100644 index 0000000..4bdc60d --- /dev/null +++ b/2021/09/README.md @@ -0,0 +1,71 @@ +# 2021 Day 09: Smoke Basin +Copyright (c) Eric Wastl +#### [Direct Link](https://adventofcode.com/2021/day/09) + +These caves seem to be [lava tubes](https://en.wikipedia.org/wiki/Lava_tube). Parts are even still volcanically active; small hydrothermal vents release smoke into the caves that slowly settles like rain. + +If you can model how the smoke flows through the caves, you might be able to avoid it and be that much safer. The submarine generates a heightmap of the floor of the nearby caves for you (your puzzle input). + +Smoke flows to the lowest point of the area it's in. For example, consider the following heightmap: + +``` +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 +``` + +Each number corresponds to the height of a particular location, where `9` is the highest and `0` is the lowest a location can be. + +Your first goal is to find the **low points** - the locations that are lower than any of its adjacent locations. Most locations have four adjacent locations (up, down, left, and right); locations on the edge or corner of the map have three or two adjacent locations, respectively. (Diagonal locations do not count as adjacent.) + +In the above example, there are **four** low points, all highlighted: two are in the first row (a `1` and a `0`), one is in the third row (a `5`), and one is in the bottom row (also a `5`). All other locations on the heightmap have some lower adjacent location, and so are not low points. + +The **risk level** of a low point is **1 plus its height**. In the above example, the risk levels of the low points are `2`, `1`, `6`, and `6`. The sum of the risk levels of all low points in the heightmap is therefore **`15`**. + +Find all of the low points on your heightmap. **What is the sum of the risk levels of all low points on your heightmap?** + +--- Part Two --- + +Next, you need to find the largest basins so you know what areas are most important to avoid. + +A **basin** is all locations that eventually flow downward to a single low point. Therefore, every low point has a basin, although some basins are very small. Locations of height `9` do not count as being in any basin, and all other locations will always be part of exactly one basin. + +The **size** of a basin is the number of locations within the basin, including the low point. The example above has four basins. + +The top-left basin, size `3`: +``` +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 +``` +The top-right basin, size `9`: +``` +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 +``` +The middle basin, size `14`: +``` +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 +``` +The bottom-right basin, size `9`: +``` +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 +``` +Find the three largest basins and multiply their sizes together. In the above example, this is `9 * 14 * 9 = 1134`. + +**What do you get if you multiply together the sizes of the three largest basins?** \ No newline at end of file diff --git a/2021/09/code.py b/2021/09/code.py new file mode 100644 index 0000000..5950db9 --- /dev/null +++ b/2021/09/code.py @@ -0,0 +1,58 @@ +# SPDX-License-Identifier: MIT +# Copyright (c) 2021 Akumatic +# +# https://adventofcode.com/2021/day/09 + +def read_file(filename: str = "input.txt") -> tuple: + with open(f"{__file__.rstrip('code.py')}{filename}", "r") as f: + lines = [line for line in f.read().strip().split("\n")] + max_x = len(lines[0]) + max_y = len(lines) + numbers = list() + for line in lines: + numbers += [int(x) for x in line] + return (max_x, max_y, numbers) + +def get_neighbors(idx: int, max_x: int, max_y: int) -> list: + neighbors = list() + if idx >= max_x: + neighbors.append(idx - max_x) + if idx < (max_x * max_y - max_x): + neighbors.append(idx + max_x) + if idx % max_x != 0: + neighbors.append(idx - 1) + if idx % max_x != (max_x - 1): + neighbors.append(idx + 1) + return neighbors + +def get_low_points(max_x, max_y, grid) -> list: + low_points = [] + for i in range(len(grid)): + if all(grid[n] > grid[i] for n in get_neighbors(i, max_x, max_y)): + low_points.append(i) + return low_points + +def expand(point, max_x, max_y, grid) -> set: + result = set() + l = {point} + while len(l) != 0: + p = l.pop() + result.add(p) + neighbors = {n for n in get_neighbors(p, max_x, max_y) if grid[n] != 9 and n not in result} + l = l.union(neighbors) + return result + +def part1(max_x, max_y, grid) -> int: + low_points = get_low_points(max_x, max_y, grid) + return sum([grid[point] for point in low_points]) + len(low_points) + +def part2(max_x, max_y, grid) -> int: + low_points = get_low_points(max_x, max_y, grid) + basin_sizes = [len(expand(point, max_x, max_y, grid)) for point in low_points] + basin_sizes.sort(reverse=True) + return basin_sizes[0] * basin_sizes[1] * basin_sizes[2] + +if __name__ == "__main__": + vals = read_file() + print(f"Part 1: {part1(*vals)}") + print(f"Part 2: {part2(*vals)}") \ No newline at end of file diff --git a/2021/09/input.txt b/2021/09/input.txt new file mode 100644 index 0000000..4d00afb --- /dev/null +++ b/2021/09/input.txt @@ -0,0 +1,100 @@ +2165679878998998656789210124569321954398786566799434678987678943987789543249654323496545436767898789 +1034598769987897545678921235698949895987676445978926799876567899876678992198966212987432325456789678 +2123987659866789756789654396987898789998543234567897989665476999865567889987654109976521012378994567 +3299878543455699967899876989876765678987632125678998976562345698754378978998543298765432123499765678 +4989865432324589878966989879985434569998545234569769987421976789653234567899955349896743276589876789 +9876954321013678989545698767894325678987654345678956798599897898732145678989876456987654387678998891 +8765985432124589995433989857895436799399795456789545459988789999546234589376987868998765678989219910 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at end of file diff --git a/2021/09/test_input.txt b/2021/09/test_input.txt new file mode 100644 index 0000000..610bad9 --- /dev/null +++ b/2021/09/test_input.txt @@ -0,0 +1,5 @@ +2199943210 +3987894921 +9856789892 +8767896789 +9899965678 \ No newline at end of file diff --git a/2021/README.md b/2021/README.md index 0f58f02..c0a7e5c 100644 --- a/2021/README.md +++ b/2021/README.md @@ -23,7 +23,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day | 06 | :white_check_mark: | :white_check_mark: | [Solution](06/code.py) | [Day 06](https://adventofcode.com/2021/day/6) | | 07 | :white_check_mark: | :white_check_mark: | [Solution](07/code.py) | [Day 07](https://adventofcode.com/2021/day/7) | | 08 | :white_check_mark: | :white_check_mark: | [Solution](08/code.py) | [Day 08](https://adventofcode.com/2021/day/8) | -| 09 | | | | | +| 09 | :white_check_mark: | :white_check_mark: | [Solution](09/code.py) | [Day 09](https://adventofcode.com/2021/day/9) | | 10 | | | | | | 11 | | | | | | 12 | | | | |