Day 15

day15/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day15"
+version = "0.1.0"

day15/input.txt

@@ -0,0 +1,32 @@
+Sensor at x=2832148, y=322979: closest beacon is at x=3015667, y=-141020
+Sensor at x=1449180, y=3883502: closest beacon is at x=2656952, y=4188971
+Sensor at x=2808169, y=1194666: closest beacon is at x=3015667, y=-141020
+Sensor at x=1863363, y=2435968: closest beacon is at x=2166084, y=2883057
+Sensor at x=3558230, y=2190936: closest beacon is at x=3244164, y=2592191
+Sensor at x=711491, y=2444705: closest beacon is at x=617239, y=2988377
+Sensor at x=2727148, y=2766272: closest beacon is at x=2166084, y=2883057
+Sensor at x=2857938, y=3988086: closest beacon is at x=2968511, y=4098658
+Sensor at x=1242410, y=2270153: closest beacon is at x=214592, y=2000000
+Sensor at x=3171784, y=2523127: closest beacon is at x=3244164, y=2592191
+Sensor at x=2293378, y=71434: closest beacon is at x=3015667, y=-141020
+Sensor at x=399711, y=73420: closest beacon is at x=1152251, y=-158441
+Sensor at x=3677529, y=415283: closest beacon is at x=3015667, y=-141020
+Sensor at x=207809, y=2348497: closest beacon is at x=214592, y=2000000
+Sensor at x=60607, y=3403420: closest beacon is at x=617239, y=2988377
+Sensor at x=3767729, y=3136725: closest beacon is at x=4171278, y=3348370
+Sensor at x=3899632, y=3998969: closest beacon is at x=4171278, y=3348370
+Sensor at x=394783, y=1541278: closest beacon is at x=214592, y=2000000
+Sensor at x=1193642, y=642631: closest beacon is at x=1152251, y=-158441
+Sensor at x=122867, y=2661904: closest beacon is at x=214592, y=2000000
+Sensor at x=551012, y=3787568: closest beacon is at x=617239, y=2988377
+Sensor at x=3175715, y=2975144: closest beacon is at x=3244164, y=2592191
+Sensor at x=402217, y=2812449: closest beacon is at x=617239, y=2988377
+Sensor at x=879648, y=1177329: closest beacon is at x=214592, y=2000000
+Sensor at x=1317218, y=2978309: closest beacon is at x=617239, y=2988377
+Sensor at x=3965126, y=1743931: closest beacon is at x=3244164, y=2592191
+Sensor at x=2304348, y=3140055: closest beacon is at x=2166084, y=2883057
+Sensor at x=3380135, y=3650709: closest beacon is at x=2968511, y=4098658
+Sensor at x=49224, y=1914296: closest beacon is at x=214592, y=2000000
+Sensor at x=3096228, y=2457233: closest beacon is at x=3244164, y=2592191
+Sensor at x=1415660, y=6715: closest beacon is at x=1152251, y=-158441
+Sensor at x=2616280, y=3548378: closest beacon is at x=2656952, y=4188971

day15/src/main.rs

@@ -1,3 +1,95 @@
-fn main() {
-    println!("Hello, world!");
+use std::{collections::HashSet, fs::read_to_string, io::Write, ops::RangeInclusive};
+
+struct Sensor {
+    x: i64,
+    y: i64,
+    x_beacon: i64,
+    y_beacon: i64,
+    distance: u64,
+}
+
+impl From<&str> for Sensor {
+    fn from(value: &str) -> Self {
+        let [x_sensor, y_sensor, x_beacon, y_beacon] = value
+            .chars()
+            .filter(|c| c.is_ascii_digit() || c.is_whitespace() || *c == '-')
+            .collect::<String>()
+            .split_whitespace()
+            .map(|n| n.parse::<i64>().unwrap())
+            .collect::<Vec<_>>()[..] else {panic!()};
+        Self {
+            x: x_sensor,
+            y: y_sensor,
+            x_beacon,
+            y_beacon,
+            distance: x_sensor.abs_diff(x_beacon) + y_sensor.abs_diff(y_beacon),
+        }
+    }
+}
+
+fn main() {
+    let input = (
+        "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"
+            .to_owned(),
+        10,
+        20,
+    );
+    let (input, line, xy_max): (_, i64, i64) = read_to_string("input.txt")
+        .map(|input| (input, 2_000_000, 4_000_000))
+        .unwrap_or(input);
+    let sensors = input.lines().map(Sensor::from).collect::<Vec<_>>();
+    let mut covered: HashSet<_> = sensors
+        .iter()
+        .flat_map(|s| {
+            let diff = line.abs_diff(s.y);
+            if diff > s.distance {
+                return RangeInclusive::new(1, 0);
+            }
+            let d = s.distance - diff;
+            (s.x - d as i64)..=(s.x + d as i64)
+        })
+        .collect();
+    for sensor in &sensors {
+        if sensor.y_beacon == line {
+            covered.remove(&sensor.x_beacon);
+        }
+    }
+    println!("{} positions can't contain a beacon", covered.len());
+    'outer: for y in 0..=xy_max {
+        let mut ranges = vec![];
+        for sensor in &sensors {
+            let diff = y.abs_diff(sensor.y);
+            if diff > sensor.distance {
+                continue;
+            }
+            let d = sensor.distance - diff;
+            ranges.push((sensor.x - d as i64)..=(sensor.x + d as i64));
+        }
+        ranges.sort_unstable_by(|r1, r2| r1.start().cmp(r2.start()));
+        let mut max_x = 0;
+        for range in ranges {
+            if max_x + 1 < *range.start() {
+                let x = max_x + 1;
+                println!(
+                    "found beacon at {x},{y} with frequency {}",
+                    x * 4_000_000 + y
+                );
+                break 'outer;
+            }
+            max_x = max_x.max(*range.end());
+        }
+    }
 }