2021: day02: quick solve

aoc2021/src/day02.rs

@@ -0,0 +1,86 @@
+use std::fmt::Write;
+
+use anyhow::{bail, Result};
+
+const INPUT: &str = include_str!("../input/day02.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+    writeln!(res, "part 2: {}", part2(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let commands = input
+        .lines()
+        .map(str::parse::<Command>)
+        .collect::<Result<Vec<_>>>()?;
+    let mut horizontal_pos = 0;
+    let mut depth = 0;
+
+    for c in commands {
+        match c {
+            Command::Forward(dx) => horizontal_pos += dx,
+            Command::Up(dz) => depth -= dz,
+            Command::Down(dz) => depth += dz,
+        }
+    }
+
+    Ok(depth * horizontal_pos)
+}
+
+fn part2(input: &str) -> Result<u64> {
+    let commands = input
+        .lines()
+        .map(str::parse::<Command>)
+        .collect::<Result<Vec<_>>>()?;
+    let mut horizontal_pos = 0;
+    let mut depth = 0;
+    let mut aim = 0;
+
+    for c in commands {
+        match c {
+            Command::Forward(dx) => {
+                horizontal_pos += dx;
+                depth += aim * dx;
+            }
+            Command::Up(dz) => {
+                aim -= dz;
+            }
+            Command::Down(dz) => {
+                aim += dz;
+            }
+        }
+    }
+
+    Ok(depth * horizontal_pos)
+}
+
+enum Command {
+    Forward(u64),
+    Up(u64),
+    Down(u64),
+}
+
+impl std::str::FromStr for Command {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let mut split = s.split(' ');
+
+        let word = split.next().unwrap();
+        let number = split.next().unwrap();
+
+        let number = number.parse()?;
+
+        Ok(match word {
+            "forward" => Self::Forward(number),
+            "up" => Self::Up(number),
+            "down" => Self::Down(number),
+            _ => bail!("unkown command"),
+        })
+    }
+}