Day 2

src/bin/day02.rs

@@ -0,0 +1,80 @@
+use color_eyre::{
+    eyre::{bail, ContextCompat},
+    Report, Result,
+};
+use std::io::stdin;
+
+fn n_colour_pair(input: &str) -> Result<(u64, &str)> {
+    let (n, c) = input
+        .trim()
+        .split_once(' ')
+        .context("Invalid poll format; expected: <num> <colour>")?;
+
+    Ok((n.parse()?, c))
+}
+
+fn part1(id: u64, game: &str) -> Result<u64> {
+    let and_reducer = |acc, x| Ok(acc && x?);
+
+    Ok(game
+        .split(';')
+        .map(|game| -> Result<bool> {
+            game.split(',')
+                .map(|poll| -> Result<bool> {
+                    let (count, colour) = n_colour_pair(poll)?;
+                    Ok(match colour {
+                        "red" if count <= 12 => true,
+                        "green" if count <= 13 => true,
+                        "blue" if count <= 14 => true,
+                        "red" | "green" | "blue" => false,
+                        c => {
+                            bail!("Invalid colour: {c}, expected red, green or blue")
+                        }
+                    })
+                })
+                .try_fold(true, and_reducer)
+        })
+        .try_fold(true, and_reducer)?
+        .then_some(id)
+        .unwrap_or_default())
+}
+
+fn part2(_: u64, game: &str) -> Result<u64> {
+    game.split([',', ';'])
+        .try_fold([0; 3], |mut acc, seg| {
+            let (count, colour) = n_colour_pair(seg)?;
+            let i = match colour {
+                "red" => 0,
+                "green" => 1,
+                "blue" => 2,
+                c => bail!("Invalid colour: {c}, expected red, green or blue"),
+            };
+
+            acc[i] = acc[i].max(count);
+            Ok(acc)
+        })
+        .map(|arr| arr.iter().product())
+}
+
+fn main() -> Result<()> {
+    //let part = part1;
+    let part = part2;
+
+    Ok(println!(
+        "{}",
+        stdin()
+            .lines()
+            .map(|ln| {
+                ln.map_err(Report::from).and_then(|ln| {
+                    let (id, game) = ln.split_once(':').context("Invalid ID")?;
+                    let id: u64 = id
+                        .strip_prefix("Game ")
+                        .context("ID should start with \"Game \"")?
+                        .parse()?;
+
+                    part(id, game)
+                })
+            })
+            .try_fold::<_, _, Result<u64>>(0, |acc, x| Ok(acc + x?))?
+    ))
+}