day 15 part 1 solution

2022/day15.txt

@@ -0,0 +1,31 @@
+Sensor at x=3923513, y=2770279: closest beacon is at x=3866712, y=2438950
+Sensor at x=675683, y=3223762: closest beacon is at x=-224297, y=2997209
+Sensor at x=129453, y=2652332: closest beacon is at x=92656, y=2629486
+Sensor at x=3906125, y=2154618: closest beacon is at x=3866712, y=2438950
+Sensor at x=65723, y=902062: closest beacon is at x=92656, y=2629486
+Sensor at x=3137156, y=2876347: closest beacon is at x=2907507, y=3100765
+Sensor at x=32848, y=2676435: closest beacon is at x=92656, y=2629486
+Sensor at x=3272472, y=3445147: closest beacon is at x=2907507, y=3100765
+Sensor at x=2926008, y=128948: closest beacon is at x=3089364, y=-501737
+Sensor at x=2975, y=2769838: closest beacon is at x=92656, y=2629486
+Sensor at x=3540455, y=2469135: closest beacon is at x=3866712, y=2438950
+Sensor at x=3674809, y=2062166: closest beacon is at x=3719980, y=2000000
+Sensor at x=3693706, y=2027384: closest beacon is at x=3719980, y=2000000
+Sensor at x=3869683, y=2291983: closest beacon is at x=3866712, y=2438950
+Sensor at x=2666499, y=2796436: closest beacon is at x=2650643, y=2489479
+Sensor at x=492, y=2601991: closest beacon is at x=92656, y=2629486
+Sensor at x=2710282, y=3892347: closest beacon is at x=2907507, y=3100765
+Sensor at x=28974, y=3971342: closest beacon is at x=-224297, y=2997209
+Sensor at x=3990214, y=2399722: closest beacon is at x=3866712, y=2438950
+Sensor at x=3853352, y=1009020: closest beacon is at x=3719980, y=2000000
+Sensor at x=1231833, y=3999338: closest beacon is at x=1313797, y=4674300
+Sensor at x=2083669, y=875035: closest beacon is at x=1369276, y=-160751
+Sensor at x=1317274, y=2146819: closest beacon is at x=2650643, y=2489479
+Sensor at x=3712875, y=2018770: closest beacon is at x=3719980, y=2000000
+Sensor at x=963055, y=23644: closest beacon is at x=1369276, y=-160751
+Sensor at x=3671967, y=64054: closest beacon is at x=3089364, y=-501737
+Sensor at x=3109065, y=2222392: closest beacon is at x=2650643, y=2489479
+Sensor at x=3218890, y=1517419: closest beacon is at x=3719980, y=2000000
+Sensor at x=3856777, y=3987650: closest beacon is at x=4166706, y=3171774
+Sensor at x=1912696, y=3392788: closest beacon is at x=2907507, y=3100765
+Sensor at x=3597620, y=3100104: closest beacon is at x=4166706, y=3171774

2022/src/days/day14.rs

@@ -9,7 +9,7 @@ enum Tile {
     Sand,
 }
 
-type Cave = [[Tile; 540]; 200];
+type Cave = [[Tile; 800]; 200];
 
 pub fn run() -> Result<()> {
     #[cfg(not(feature = "test_input"))]
@@ -18,7 +18,7 @@ pub fn run() -> Result<()> {
     #[cfg(feature = "test_input")]
     let file_contents = fs::read_to_string("tests/day14.txt")?;
 
-    let mut cave: Cave = [[Tile::Air; 540]; 200];
+    let mut cave: Cave = [[Tile::Air; 800]; 200];
     cave[0][500] = Tile::Source;
     let mut minx = 520;
     let mut maxx = 500;
@@ -76,8 +76,8 @@ pub fn run() -> Result<()> {
         }
     }
 
-    //print_cave(&cave, minx, 0, maxx, maxy);
     part1_sand_units(&cave, minx, maxx, maxy);
+    part2_sand_units(&cave, maxy);
 
     Ok(())
 }
@@ -134,23 +134,31 @@ fn part1_sand_units(c: &Cave, minx: usize, maxx: usize, maxy: usize) {
     print_cave(&cave, minx, 0, maxx, maxy);
 }
 
-fn part2_sand_units(c: &Cave, minx: usize, maxx: usize, maxy: usize) {
+fn part2_sand_units(c: &Cave, maxy: usize) {
     let mut cave = c.clone();
     let mut units = 0;
+    let mut minx = 800;
+    let mut maxx = 0;
 
     let floor = maxy + 2;
-    for i in 0..540 {
+    for i in 0..800 {
         cave[floor][i] = Tile::Rock;
     }
 
     loop {
-        if let Tile::Sand = cave[500][0] {
+        if let Tile::Sand = cave[0][500] {
             break;
         }
         let mut x = 500;
         let mut placed = false;
         for i in 0..floor {
             if placed {
+                if x < minx {
+                    minx = x;
+                }
+                if x > maxx {
+                    maxx = x;
+                }
                 break;
             }
             match cave[i + 1][x] {
@@ -164,7 +172,6 @@ fn part2_sand_units(c: &Cave, minx: usize, maxx: usize, maxy: usize) {
                     } else {
                         placed = true;
                         cave[i][x] = Tile::Sand;
-                        break;
                     }
                 }
             }
@@ -176,5 +183,5 @@ fn part2_sand_units(c: &Cave, minx: usize, maxx: usize, maxy: usize) {
         }
     }
     println!("part two units {}", units);
-    print_cave(&cave, minx, 0, maxx, maxy);
+    print_cave(&cave, minx, 0, maxx, floor);
 }

2022/src/days/day15.rs

@@ -0,0 +1,83 @@
+use anyhow::Result;
+use std::fs;
+use std::collections::HashSet;
+
+#[derive(Debug)]
+struct Pair {
+    sensor: Coord,
+    beacon: Coord,
+}
+
+#[derive(Debug, Eq, Hash, PartialEq)]
+struct Coord {
+    x: i32,
+    y: i32,
+}
+
+impl Pair {
+    fn distance(self: &Self) -> i32 {
+        (self.sensor.x - self.beacon.x).abs() + (self.sensor.y - self.beacon.y).abs()
+    }
+}
+
+pub fn run() -> Result<()> {
+    #[cfg(not(feature = "test_input"))]
+    let file_contents = fs::read_to_string("day15.txt")?;
+
+    #[cfg(feature = "test_input")]
+    let file_contents = fs::read_to_string("tests/day15.txt")?;
+
+    let mut pairs: Vec<Pair> = Vec::with_capacity(25);
+
+    for line in file_contents.lines() {
+        let mut parts = line.split(": ");
+        let spart = parts.next().unwrap().strip_prefix("Sensor at ").unwrap();
+        let bpart = parts.next().unwrap().strip_prefix("closest beacon is at ").unwrap();
+        let mut scoords = spart.split(", ");
+        let sx = scoords.next().unwrap().strip_prefix("x=").unwrap().parse::<i32>().unwrap();
+        let sy = scoords.next().unwrap().strip_prefix("y=").unwrap().parse::<i32>().unwrap();
+        let mut bcoords = bpart.split(", ");
+        let bx = bcoords.next().unwrap().strip_prefix("x=").unwrap().parse::<i32>().unwrap();
+        let by = bcoords.next().unwrap().strip_prefix("y=").unwrap().parse::<i32>().unwrap();
+        pairs.push(Pair {
+            sensor: Coord { x: sx, y: sy },
+            beacon: Coord { x: bx, y: by },
+        });
+    }
+
+    #[cfg(not(feature = "test_input"))]
+    spots_taken_on_row(&pairs, 2000000);
+
+    #[cfg(feature = "test_input")]
+    spots_taken_on_row(&pairs, 10);
+
+//    println!("pairs {:?}", pairs);
+    Ok(())
+}
+
+fn spots_taken_on_row(pairs: &Vec<Pair>, row: i32) {
+    let mut c: HashSet<i32> = HashSet::new();
+    for p in pairs.iter() {
+        let d = p.distance();
+        if row > p.sensor.y && row - p.sensor.y > d {
+            continue;
+        } else if row < p.sensor.y && p.sensor.y - row > d {
+            continue;
+        }
+        let remaining_distance = d - (row - p.sensor.y).abs();
+        let minx = p.sensor.x - remaining_distance;
+        let maxx = p.sensor.x + remaining_distance;
+//        println!("{:?} distance {} from {}..={}", p.sensor, d, minx, maxx);
+        for x in minx..=maxx {
+            c.insert(x);
+        }
+    }
+
+    for p in pairs.iter() {
+        if p.beacon.y == row {
+            c.remove(&p.beacon.x);
+        }
+    }
+
+    println!("spots taken on row {} = {}", row, c.len());
+}

2022/src/days/mod.rs

@@ -4,6 +4,7 @@ pub mod day11;
 pub mod day12;
 pub mod day13;
 pub mod day14;
+pub mod day15;
 pub mod day2;
 pub mod day3;
 pub mod day4;

2022/src/main.rs

@@ -54,6 +54,9 @@ fn run_day(number: i32) -> Result<()> {
         14 => {
             days::day14::run()?;
         }
+        15 => {
+            days::day15::run()?;
+        }
         _ => return Err(anyhow!("Invalid day provided")),
     }
     Ok(())

2022/tests/day15.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