Implement 2022 day 15 part 2

2022/inputs/15.txt

@@ -0,0 +1,24 @@
+Sensor at x=3988693, y=3986119: closest beacon is at x=3979063, y=3856315
+Sensor at x=1129181, y=241785: closest beacon is at x=1973630, y=-98830
+Sensor at x=2761889, y=2453622: closest beacon is at x=2803715, y=2643139
+Sensor at x=3805407, y=3099635: closest beacon is at x=3744251, y=2600851
+Sensor at x=3835655, y=3999745: closest beacon is at x=3979063, y=3856315
+Sensor at x=3468377, y=3661078: closest beacon is at x=3979063, y=3856315
+Sensor at x=1807102, y=3829998: closest beacon is at x=2445544, y=3467698
+Sensor at x=2774374, y=551040: closest beacon is at x=1973630, y=-98830
+Sensor at x=2004588, y=2577348: closest beacon is at x=2803715, y=2643139
+Sensor at x=2949255, y=3611925: closest beacon is at x=2445544, y=3467698
+Sensor at x=2645982, y=3991988: closest beacon is at x=2445544, y=3467698
+Sensor at x=3444780, y=2880445: closest beacon is at x=3744251, y=2600851
+Sensor at x=3926452, y=2231046: closest beacon is at x=3744251, y=2600851
+Sensor at x=3052632, y=2882560: closest beacon is at x=2803715, y=2643139
+Sensor at x=3994992, y=2720288: closest beacon is at x=3744251, y=2600851
+Sensor at x=3368581, y=1443706: closest beacon is at x=3744251, y=2600851
+Sensor at x=2161363, y=1856161: closest beacon is at x=1163688, y=2000000
+Sensor at x=3994153, y=3414445: closest beacon is at x=3979063, y=3856315
+Sensor at x=2541906, y=2965730: closest beacon is at x=2803715, y=2643139
+Sensor at x=600169, y=3131140: closest beacon is at x=1163688, y=2000000
+Sensor at x=163617, y=1082438: closest beacon is at x=1163688, y=2000000
+Sensor at x=3728368, y=140105: closest beacon is at x=3732654, y=-724773
+Sensor at x=1187681, y=2105247: closest beacon is at x=1163688, y=2000000
+Sensor at x=2327144, y=3342616: closest beacon is at x=2445544, y=3467698

2022/src/common.rs

@@ -1,6 +1,11 @@
 //! Common helper utilities to all days
 
 use std::cmp::Ordering;
+use std::ops::Add;
+use std::ops::Div;
+use std::ops::Index;
+use std::ops::IndexMut;
+use std::ops::Sub;
 
 use anyhow::Result;
 use nom::combinator::map;
@@ -172,3 +177,52 @@ impl IndexSet {
         }
     }
 }
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Vec2(pub [i32; 2]);
+
+impl Vec2 {
+    pub fn l1(self) -> i32 {
+        self.0.into_iter().map(i32::abs).sum()
+    }
+}
+
+impl Add<Self> for Vec2 {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self([self[0] + rhs[0], self[1] + rhs[1]])
+    }
+}
+
+impl Sub<Self> for Vec2 {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self([self[0] - rhs[0], self[1] - rhs[1]])
+    }
+}
+
+impl Div<i32> for Vec2 {
+    type Output = Self;
+
+    fn div(self, rhs: i32) -> Self::Output {
+        Self(self.0.map(|v| v / rhs))
+    }
+}
+
+impl Index<usize> for Vec2 {
+    type Output = i32;
+
+    #[inline]
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.0[index]
+    }
+}
+
+impl IndexMut<usize> for Vec2 {
+    #[inline]
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        &mut self.0[index]
+    }
+}

2022/src/day09.rs

@@ -1,8 +1,3 @@
-use std::ops::Add;
-use std::ops::Index;
-use std::ops::IndexMut;
-use std::ops::Sub;
-
 use ahash::AHashSet;
 use anyhow::Result;
 use nom::bytes::complete::tag;
@@ -15,6 +10,7 @@ use nom::sequence::terminated;
 use nom::IResult;
 
 use crate::common::parse_input;
+use crate::common::Vec2;
 
 #[derive(Copy, Clone)]
 enum Direction {
@@ -60,41 +56,6 @@ fn parse_moves(input: &[u8]) -> IResult<&[u8], Vec<(Direction, u32)>> {
     ))(input)
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
-struct Vec2(pub [i32; 2]);
-
-impl Add<Self> for Vec2 {
-    type Output = Self;
-
-    fn add(self, rhs: Self) -> Self::Output {
-        Self([self[0] + rhs[0], self[1] + rhs[1]])
-    }
-}
-
-impl Sub<Self> for Vec2 {
-    type Output = Self;
-
-    fn sub(self, rhs: Self) -> Self::Output {
-        Self([self[0] - rhs[0], self[1] - rhs[1]])
-    }
-}
-
-impl Index<usize> for Vec2 {
-    type Output = i32;
-
-    #[inline]
-    fn index(&self, index: usize) -> &Self::Output {
-        &self.0[index]
-    }
-}
-
-impl IndexMut<usize> for Vec2 {
-    #[inline]
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        &mut self.0[index]
-    }
-}
-
 fn part_generic<const N: usize>(input: &[u8]) -> Result<String> {
     let moves = parse_input(input, parse_moves)?;
 

2022/src/day14.rs

@@ -91,7 +91,7 @@ fn parse_cave(input: &[u8]) -> IResult<&[u8], Cave> {
 
     let mut input = input;
 
-    while input != &[][..] {
+    while input != &b""[..] {
         let new_input = terminated(
             reduce_many1(
                 terminated(parse_pair, opt(tag(" -> "))),

2022/src/day15.rs

@@ -1,9 +1,178 @@
+use std::cmp::Reverse;
+use std::collections::BinaryHeap;
+
+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;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use crate::common::parse_input;
+use crate::common::Vec2;
+
+struct Beacon {
+    pos: Vec2,
+    closest: Vec2,
+    range: i32,
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+impl Beacon {
+    pub fn can_contain_unseen(&self, lower: Vec2, upper: Vec2) -> bool {
+        let corners = [
+            lower,
+            upper,
+            Vec2([lower[0], upper[1]]),
+            Vec2([upper[0], lower[1]]),
+        ];
+
+        corners
+            .into_iter()
+            .any(|c| (c - self.pos).l1() > self.range)
+    }
+}
+
+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,
+            range: (pos - closest).l1(),
+        },
+    );
+
+    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 horizontal_distance = beacon.range - (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)
+}
+
+fn part2_generic<const MAX: i32>(input: &[u8]) -> Result<String> {
+    let beacons = parse_input(input, parse_beacons)?;
+
+    fn find_unseen<const MAX: i32>(beacons: &[Beacon]) -> Result<Vec2> {
+        let mut todo = vec![(Vec2([0, 0]), Vec2([MAX, MAX]))];
+
+        while let Some((lower, upper)) = todo.pop() {
+            if lower == upper {
+                if beacons
+                    .iter()
+                    .all(|beacon| (beacon.pos - lower).l1() > beacon.range)
+                {
+                    return Ok(lower);
+                }
+            } else {
+                let mid = (lower + upper) / 2;
+
+                let quads = [
+                    (lower, mid),
+                    (Vec2([lower[0], mid[1] + 1]), Vec2([mid[0], upper[1]])),
+                    (Vec2([mid[0] + 1, lower[1]]), Vec2([upper[0], mid[1]])),
+                    (Vec2([mid[0] + 1, mid[1] + 1]), upper),
+                ];
+
+                for (lower_new, upper_new) in quads {
+                    if lower_new[0] > upper_new[0] || lower_new[1] > upper_new[1] {
+                        // Empty quad in quad tree, skip
+                    } else if beacons
+                        .iter()
+                        .all(|beacon| beacon.can_contain_unseen(lower_new, upper_new))
+                    {
+                        todo.push((lower_new, upper_new));
+                    }
+                }
+            }
+        }
+
+        anyhow::bail!("Did not find position")
+    }
+
+    let Vec2([x, y]) = find_unseen::<MAX>(&beacons)?;
+
+    Ok((i64::from(x) * 4000000 + i64::from(y)).to_string())
+}
+
+pub fn part2(input: &[u8]) -> Result<String> {
+    part2_generic::<4000000>(input)
+}
+
+#[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");
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2_generic::<20>(SAMPLE).unwrap(), "56000011");
+    }
 }

2022/src/main.rs

@@ -56,6 +56,6 @@ fn main() -> Result<()> {
         eprintln!("Execution time: {:?}", Instant::now().duration_since(begin));
     }
 
-    println!("{}", result);
+    println!("{result}");
     Ok(())
 }

2022/src/samples/15.txt

@@ -0,0 +1,14 @@
+Sensor at x=2, y=18: closest beacon is at x=-2, y=15
+Sensor at x=9, y=16: closest beacon is at x=10, y=16
+Sensor at x=13, y=2: closest beacon is at x=15, y=3
+Sensor at x=12, y=14: closest beacon is at x=10, y=16
+Sensor at x=10, y=20: closest beacon is at x=10, y=16
+Sensor at x=14, y=17: closest beacon is at x=10, y=16
+Sensor at x=8, y=7: closest beacon is at x=2, y=10
+Sensor at x=2, y=0: closest beacon is at x=2, y=10
+Sensor at x=0, y=11: closest beacon is at x=2, y=10
+Sensor at x=20, y=14: closest beacon is at x=25, y=17
+Sensor at x=17, y=20: closest beacon is at x=21, y=22
+Sensor at x=16, y=7: closest beacon is at x=15, y=3
+Sensor at x=14, y=3: closest beacon is at x=15, y=3
+Sensor at x=20, y=1: closest beacon is at x=15, y=3