Day 3

src/day03.rs

@@ -0,0 +1,101 @@
+use std::str::FromStr;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[derive(Debug, Default)]
+pub struct Rucksack {
+    first_half: Vec<u8>,
+    second_half: Vec<u8>,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct NoItemInBothHalves;
+
+#[derive(Debug, Copy, Clone)]
+pub struct NoCommonItem;
+
+impl Rucksack {
+    fn find_item_in_both_halves(&self) -> Result<u8, NoItemInBothHalves> {
+        for &item in &self.first_half {
+            if self.second_half.contains(&item) {
+                return Ok(item);
+            }
+        }
+        Err(NoItemInBothHalves)
+    }
+
+    fn has_item(&self, item: u8) -> bool {
+        self.first_half.contains(&item) | self.second_half.contains(&item)
+    }
+
+    fn find_common_item(&self, others: &[Rucksack]) -> Result<u8, NoCommonItem> {
+        for &item in self.first_half.iter().chain(&self.second_half) {
+            if others.iter().all(|rucksack| rucksack.has_item(item)) {
+                return Ok(item);
+            }
+        }
+        Err(NoCommonItem)
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct InvalidRucksack;
+
+impl FromStr for Rucksack {
+    type Err = InvalidRucksack;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut priorities = s
+            .chars()
+            .map(|ch| {
+                if !ch.is_ascii_alphabetic() {
+                    Err(InvalidRucksack)
+                } else if ch.is_ascii_uppercase() {
+                    Ok(ch as u8 - b'A' + 27)
+                } else {
+                    Ok(ch as u8 - b'a' + 1)
+                }
+            })
+            .collect::<Result<Vec<_>, _>>()?;
+        let second_half = priorities.split_off(priorities.len() / 2);
+        Ok(Rucksack {
+            first_half: priorities,
+            second_half,
+        })
+    }
+}
+
+#[aoc_generator(day3, part1)]
+pub fn input_generator_part1(input: &str) -> Vec<Rucksack> {
+    input.lines().map(|l| l.parse().unwrap()).collect()
+}
+
+#[aoc_generator(day3, part2)]
+pub fn input_generator_part2(input: &str) -> Vec<Vec<Rucksack>> {
+    input
+        .lines()
+        .collect::<Vec<_>>()
+        .chunks(3)
+        .map(|list| {
+            list.iter()
+                .map(|el| el.parse().unwrap())
+                .collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>()
+}
+
+#[aoc(day3, part1)]
+pub fn solve_part1(input: &[Rucksack]) -> u64 {
+    input
+        .iter()
+        .map(|rucksack| rucksack.find_item_in_both_halves().unwrap() as u64)
+        .sum()
+}
+
+#[aoc(day3, part2)]
+pub fn solve_part2(input: &[Vec<Rucksack>]) -> u64 {
+    input
+        .iter()
+        .map(|rucksacks| rucksacks[0].find_common_item(&rucksacks[1..]).unwrap() as u64)
+        .sum()
+}

src/lib.rs

@@ -2,5 +2,6 @@ use aoc_runner_derive::aoc_lib;
 
 pub mod day01;
 pub mod day02;
+pub mod day03;
 
 aoc_lib! { year = 2022 }