Implement 2022 day 3

2022/src/day03.rs

@@ -1,9 +1,79 @@
 use anyhow::Result;
+use itertools::Itertools;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    todo!()
+fn priority(item: u8) -> u32 {
+    match item {
+        b'a'..=b'z' => item - b'a' + 1,
+        b'A'..=b'Z' => item - b'A' + 27,
+        _ => 0,
+    }
+    .into()
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    todo!()
+fn seen(backpack: &[u8]) -> u64 {
+    let mut seen = 0;
+
+    for &b in backpack {
+        seen |= 1 << priority(b);
+    }
+
+    seen
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let mut total = 0;
+
+    for line in input.split(|&b| b == b'\n') {
+        let (first, last) = line.split_at(line.len() / 2);
+
+        let seen = seen(first);
+
+        for &b in last {
+            let prio = priority(b);
+
+            if (seen & (1 << prio)) != 0 {
+                total += prio;
+                break;
+            }
+        }
+    }
+
+    Ok(total.to_string())
+}
+
+pub fn part2(input: &[u8]) -> Result<String> {
+    let mut total = 0;
+
+    for chunk in &input.split(|&b| b == b'\n').chunks(3) {
+        let mut mask = u64::MAX;
+
+        for backpack in chunk {
+            let seen = seen(backpack);
+            mask &= seen;
+        }
+
+        if mask != 0 {
+            debug_assert_eq!(1, mask.count_ones());
+            total += mask.trailing_zeros();
+        }
+    }
+
+    Ok(total.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/03.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "157")
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "70")
+    }
 }

2022/src/samples/03.txt

@@ -0,0 +1,6 @@
+vJrwpWtwJgWrhcsFMMfFFhFp
+jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
+PmmdzqPrVvPwwTWBwg
+wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
+ttgJtRGJQctTZtZT
+CrZsJsPPZsGzwwsLwLmpwMDw