[rs] Solve 2022_15 part 1

rs/src/main.rs

@@ -65,6 +65,7 @@ days! {
     Y2022D12: "2022_12" => y2022::d12::solve,
     Y2022D13: "2022_13" => y2022::d13::solve,
     Y2022D14: "2022_14" => y2022::d14::solve,
+    Y2022D15: "2022_15" => y2022::d15::solve,
 }
 
 #[derive(Parser)]

rs/src/y2022.rs

@@ -12,3 +12,4 @@ pub mod d11;
 pub mod d12;
 pub mod d13;
 pub mod d14;
+pub mod d15;

rs/src/y2022/d15.rs

@@ -0,0 +1,52 @@
+use std::collections::HashSet;
+
+struct Sensor {
+    pos: (i32, i32),
+    beac: (i32, i32),
+    dist: i32,
+}
+
+fn parse_coord(coord: &str) -> i32 {
+    let coord = coord.replace(|c| "xy=,:".contains(c), "");
+    coord.parse().unwrap()
+}
+
+pub fn solve(input: String) {
+    let sensors = input
+        .lines()
+        .map(|l| {
+            let parts = l.split_whitespace().collect::<Vec<_>>();
+            let pos = (parse_coord(parts[2]), parse_coord(parts[3]));
+            let beac = (parse_coord(parts[8]), parse_coord(parts[9]));
+            let dist = (pos.0 - beac.0).abs() + (pos.1 - beac.1).abs();
+            Sensor { pos, beac, dist }
+        })
+        .collect::<Vec<_>>();
+
+    // A beacon exactly dist away has 1 field, i. e. x±0
+    // A beacon exactly dist-1 away has 3 fields, i. e. x±1
+    // ...
+    // A beacon exactly 0 away has 2dist+1 fields, i. e. x±dist
+    //
+    // Formula: Go from x-(dist-dy) to x+(dist-dy)
+    let line_at_y = 2000000;
+    let mut part1 = HashSet::new();
+    for (i, sensor) in sensors.iter().enumerate() {
+        eprintln!("Sensor {}", i + 1);
+        let dy = (line_at_y - sensor.pos.1).abs();
+        if dy > sensor.dist {
+            continue;
+        }
+
+        let dx = sensor.dist - dy;
+        for x in (sensor.pos.0 - dx)..=(sensor.pos.0 + dx) {
+            part1.insert(x);
+        }
+    }
+    for sensor in &sensors {
+        if sensor.beac.1 == line_at_y {
+            part1.remove(&sensor.beac.0);
+        }
+    }
+    println!("Part 1: {}", part1.len());
+}