2022 Day 15: Part 1

2022/src/bin/day15.rs

@@ -0,0 +1,101 @@
+use std::collections::HashSet;
+
+use regex::Regex;
+
+const INPUT: &str = include_str!("../../input/day15.txt");
+
+fn main() {
+    println!("{}", part1(INPUT, 2_000_000));
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+struct Pos {
+    x: i32,
+    y: i32,
+}
+
+impl std::fmt::Display for Pos {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "({}, {})", self.x, self.y)
+    }
+}
+
+impl Pos {
+    fn new(x: i32, y: i32) -> Self {
+        Self { x, y }
+    }
+
+    fn distance(&self, other: Pos) -> i32 {
+        let dx = self.x - other.x;
+        let dy = self.y - other.y;
+        dx.abs() + dy.abs()
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+struct Sensor {
+    pos: Pos,
+}
+
+#[derive(Debug, Copy, Clone)]
+struct Beacon {
+    pos: Pos,
+}
+
+fn part1(input: &str, yy: i32) -> usize {
+    let pairs: Vec<(Sensor, Beacon)> = aoc::lines(input).map(parse_line).collect();
+
+    let relevant: Vec<(Sensor, Beacon)> = pairs
+        .iter()
+        .cloned()
+        .filter(|(s, b)| {
+            let d_cover = s.pos.distance(b.pos);
+            let d_line = s.pos.distance(Pos::new(s.pos.x, yy));
+            d_line <= d_cover
+        })
+        .collect();
+
+    let mut coverage: HashSet<Pos> = HashSet::new();
+
+    for (s, b) in relevant {
+        let d_cover = s.pos.distance(b.pos);
+        let d_line = s.pos.distance(Pos::new(s.pos.x, yy));
+        let w_line = d_cover - d_line;
+
+        let x = s.pos.x;
+        for dx in 0..=w_line {
+            coverage.insert(Pos::new(x + dx, yy));
+            coverage.insert(Pos::new(x - dx, yy));
+        }
+    }
+
+    for (_, b) in pairs {
+        coverage.remove(&b.pos);
+    }
+
+    coverage.len()
+}
+
+fn parse_line(line: &str) -> (Sensor, Beacon) {
+    let re = Regex::new(
+        r"Sensor at x=(?P<sx>.*), y=(?P<sy>.*): closest beacon is at x=(?P<bx>.*), y=(?P<by>.*)",
+    )
+    .unwrap();
+
+    let caps = re.captures(line).unwrap();
+
+    (
+        Sensor {
+            pos: Pos {
+                x: caps.name("sx").unwrap().as_str().parse().unwrap(),
+                y: caps.name("sy").unwrap().as_str().parse().unwrap(),
+            },
+        },
+        Beacon {
+            pos: Pos {
+                x: caps.name("bx").unwrap().as_str().parse().unwrap(),
+                y: caps.name("by").unwrap().as_str().parse().unwrap(),
+            },
+        },
+    )
+}