Day 2 part 1.

2021/src/day2.rs

@@ -0,0 +1,79 @@
+//! --- Day 2: Dive! ---
+//! 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?
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[aoc(day2, part1)]
+fn part1(input: &str) -> i32 {
+    let mut horizontal: i32 = 0;
+    let mut depth: i32 = 0;
+    input.split("\n").for_each(|l| {
+        let p: Vec<_> = l.split(" ").collect();
+
+        match p[0] {
+            "forward" => horizontal += p[1].parse::<i32>().expect("forward"),
+            "up" => depth -= p[1].parse::<i32>().expect("up"),
+            "down" => depth += p[1].parse::<i32>().expect("down"),
+            _ => panic!("unknown command {}", p[0]),
+        }
+    });
+    horizontal * depth
+}
+
+/*
+#[aoc(day2, part2)]
+fn part2(depths: &[u32]) -> u32 {
+todo!("part2")
+}
+*/
+
+#[test]
+fn test_part1() {
+    let input = r#"
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2
+"#
+    .trim();
+    assert_eq!(part1(input), 150);
+}
+
+/*
+#[test]
+fn test_part2() {
+let input = r#"
+"#
+.trim();
+assert_eq!(part2(&parse(input)), TODO);
+}
+*/

2021/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod day1;
+pub mod day2;
 
 use aoc_runner_derive::aoc_lib;