2021 Day 02

2021/02/README.md

@@ -0,0 +1,66 @@
+# 2021 Day 02: Dive!
+Copyright (c) Eric Wastl
+#### [Direct Link](https://adventofcode.com/2021/day/02)
+
+## Part 1
+
+Now, you need to figure out how to pilot this thing.
+
+It seems like the submarine can take a series of commands like `forward 1`, `down 2`, or `up 3`:
+
+- `forward X` increases the horizontal position by `X` units.
+- `down X` **increases** the depth by `X` units.
+- `up X` **decreases** the depth by `X` units.
+
+Note that since you're on a submarine, `down` and `up` affect your **depth**, and so they have the opposite result of what you might expect.
+
+The submarine seems to already have a planned course (your puzzle input). You should probably figure out where it's going. For example:
+
+```
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2
+```
+
+Your horizontal position and depth both start at `0`. The steps above would then modify them as follows:
+
+- `forward 5` adds `5` to your horizontal position, a total of `5`.
+- `down 5` adds `5` to your depth, resulting in a value of `5`.
+- `forward 8` adds `8` to your horizontal position, a total of `13`.
+- `up 3` decreases your depth by `3`, resulting in a value of `2`.
+- `down 8` adds `8` to your depth, resulting in a value of `10`.
+- `forward 2` adds `2` to your horizontal position, a total of `15`.
+
+After following these instructions, you would have a horizontal position of `15` and a depth of `10`. (Multiplying these together produces **`150`**.)
+
+Calculate the horizontal position and depth you would have after following the planned course. `What do you get if you multiply your final horizontal position by your final depth?`
+
+## Part 2
+
+Based on your calculations, the planned course doesn't seem to make any sense. You find the submarine manual and discover that the process is actually slightly more complicated.
+
+In addition to horizontal position and depth, you'll also need to track a third value, **aim**, which also starts at `0`. The commands also mean something entirely different than you first thought:
+
+- `down X` **increases** your aim by `X` units.
+- `up X` **decreases** your aim by `X` units.
+- `forward X` does two things:
+    - It increases your horizontal position by `X` units.
+    - It increases your depth by your aim **multiplied by** `X`.
+
+Again note that since you're on a submarine, `down` and `up` do the opposite of what you might expect: "down" means aiming in the positive direction.
+
+Now, the above example does something different:
+
+- `forward 5` adds `5` to your horizontal position, a total of `5`. Because your aim is `0`, your depth does not change.
+- `down 5` adds `5` to your aim, resulting in a value of `5`.
+- `forward 8` adds `8` to your horizontal position, a total of `13`. Because your aim is `5`, your depth increases by `8*5=40`.
+- `up 3` decreases your aim by `3`, resulting in a value of `2`.
+- `down 8` adds `8` to your aim, resulting in a value of `10`.
+- `forward 2` adds `2` to your horizontal position, a total of `15`. Because your aim is `10`, your depth increases by `2*10=20` to a total of `60`.
+
+After following these new instructions, you would have a horizontal position of `15` and a depth of `60`. (Multiplying these produces **`900`**.)
+
+Using this new interpretation of the commands, calculate the horizontal position and depth you would have after following the planned course. **What do you get if you multiply your final horizontal position by your final depth?**

2021/02/code.py

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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+#
+# https://adventofcode.com/2021/day/02
+
+def read_file() -> list:
+    with open(f"{__file__.rstrip('code.py')}input.txt", "r") as f:
+        return [(s[0], int(s[1])) for s in (line.split() for line in f.read().strip().split("\n"))]
+
+def part1(commands: list) -> int:
+    position, depth = 0, 0
+    for com in commands:
+        if com[0] == "forward":
+            position += com[1]
+        elif com[0] == "down":
+            depth += com[1]
+        else: #com[1] == "up"
+            depth -= com[1]
+    return position * depth
+            
+
+def part2(commands: list) -> int:
+    position, depth, aim = 0, 0, 0
+    for com in commands:
+        if com[0] == "forward":
+            position += com[1]
+            depth += aim * com[1]
+        elif com[0] == "down":
+            aim += com[1]
+        else: #com[1] == "up"
+            aim -= com[1]
+    return position * depth
+
+if __name__ == "__main__":
+    vals = read_file()
+    print(f"Part 1: {part1(vals)}")
+    print(f"Part 2: {part2(vals)}")

2021/02/solution.txt

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+Part 1: 1648020
+Part 2: 1759818555

2021/02/test_code.py

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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+
+from code import part1, part2
+
+def test():
+    vals = [("forward", 5), ("down", 5), ("forward", 8), ("up", 3), ("down", 8), ("forward", 2)]
+    assert part1(vals) == 150
+    print("Passed Part 1")
+    assert part2(vals) == 900
+    print("Passed Part 2")
+
+if __name__ == "__main__":
+    test()

2021/README.md

@@ -16,7 +16,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 | Day | Part 1 | Part 2 | My Solution | Official Website | 
 | --- | --- | --- |---| --- |
 | 01 | :white_check_mark: | :white_check_mark: | [Solution](01/code.py) | [Day 01](https://adventofcode.com/2021/day/1) |
-| 02 |  |  |  |  |
+| 02 | :white_check_mark: | :white_check_mark: | [Solution](02/code.py) | [Day 02](https://adventofcode.com/2021/day/2) |
 | 03 |  |  |  |  |
 | 04 |  |  |  |  |
 | 05 |  |  |  |  |