Implement 2022 day 15 part 1

2022/src/day15.rs

@@ -1,9 +1,109 @@
-use anyhow::Result;
+use std::cmp::Reverse;
+use std::collections::BinaryHeap;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use ahash::AHashSet;
+use anyhow::Result;
+use nom::bytes::complete::tag;
+use nom::character::complete::newline;
+use nom::combinator::map;
+use nom::multi::many0;
+use nom::sequence::pair;
+use nom::sequence::preceded;
+use nom::sequence::terminated;
+use nom::IResult;
+
+use crate::common::parse_input;
+use crate::common::Vec2;
+
+struct Beacon {
+    pos: Vec2,
+    closest: Vec2,
+}
+
+fn parse_pos(input: &[u8]) -> IResult<&[u8], Vec2> {
+    use nom::character::complete::i32;
+    map(
+        pair(preceded(tag("x="), i32), preceded(tag(", y="), i32)),
+        |(x, y)| Vec2([x, y]),
+    )(input)
+}
+
+fn parse_beacons(input: &[u8]) -> IResult<&[u8], Vec<Beacon>> {
+    let parse_beacon = map(
+        pair(
+            preceded(tag("Sensor at "), parse_pos),
+            preceded(tag(": closest beacon is at "), parse_pos),
+        ),
+        |(pos, closest)| Beacon { pos, closest },
+    );
+
+    many0(terminated(parse_beacon, newline))(input)
+}
+
+fn part1_generic<const Y: i32>(input: &[u8]) -> Result<String> {
+    let beacons = parse_input(input, parse_beacons)?;
+
+    let mut not_blocking_yet = BinaryHeap::new();
+    let mut blocking = BinaryHeap::new();
+
+    let mut total = 0;
+
+    let mut on_line = AHashSet::new();
+
+    for beacon in beacons {
+        let distance = (beacon.closest - beacon.pos).l1();
+        let horizontal_distance = distance - (beacon.pos[1] - Y).abs();
+
+        if horizontal_distance >= 0 {
+            not_blocking_yet.push(Reverse((
+                beacon.pos[0] - horizontal_distance,
+                beacon.pos[0] + horizontal_distance + 1,
+            )))
+        }
+
+        // Beacons can be beacons, so we should uncount them
+        if beacon.closest[1] == Y {
+            on_line.insert(beacon.closest);
+        }
+    }
+
+    while let Some(Reverse((block_from, mut block_until))) = not_blocking_yet.pop() {
+        blocking.push(Reverse(block_until));
+
+        while let Some(Reverse(block_end)) = blocking.pop() {
+            block_until = block_until.max(block_end);
+
+            while matches!(not_blocking_yet.peek(), Some(Reverse((block_from, _))) if block_from < &block_end)
+            {
+                let Reverse((_, additional_block_until)) = not_blocking_yet.pop().unwrap();
+                blocking.push(Reverse(additional_block_until));
+            }
+        }
+
+        total += block_until - block_from;
+    }
+
+    total -= on_line.len() as i32;
+
+    Ok(total.to_string())
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    part1_generic::<2000000>(input)
 }
 
 pub fn part2(_input: &[u8]) -> Result<String> {
     anyhow::bail!("not implemented")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/15.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1_generic::<10>(SAMPLE).unwrap(), "26");
+    }
+}