1 files changed, 102 insertions, 0 deletions
diff --git a/2019/src/bin/day_19.rs b/2019/src/bin/day_19.rs
new file mode 100644
index 0000000..73c8374
--- /dev/null
+++ b/2019/src/bin/day_19.rs
@@ -0,0 +1,102 @@
+use aoc2019::*;
+use cached::cached_key;
+use cached::UnboundCache;
+use rpds::list;
+use rpds::list::List;
+use rpds::vector;
+use std::io;
+use std::io::prelude::*;
+use std::process;
+use structopt::StructOpt;
+
+#[derive(Debug, StructOpt)]
+#[structopt(name = "Day 19: Tractor Beam")]
+/// Finds the effective area of a tractor beam in an n x n square, and
+/// how far away you need to be to capture Santa's ship.
+///
+/// See https://adventofcode.com/2019/day/19 for details.
+struct Opt {
+    /// The size for a diagnostics scan.
+    #[structopt(long = "diagnostics-size")]
+    diagnostics_size: Option<usize>,
+    /// The size of Santa's ship
+    #[structopt(long = "ship-size")]
+    ship_size: Option<usize>,
+}
+
+fn main() {
+    let stdin = io::stdin();
+    let opt = Opt::from_args();
+
+    let program: IntcodeProgram = stdin
+        .lock()
+        .split(b',')
+        .map(|x| exit_on_failed_assertion(x, "Error reading input"))
+        .map(|x| exit_on_failed_assertion(String::from_utf8(x), "Input was not valid UTF-8"))
+        .map(|x| exit_on_failed_assertion(x.trim().parse::<Intcode>(), "Invalid number"))
+        .collect::<IntcodeProgram>();
+
+    if let Some(size) = opt.diagnostics_size {
+        println!("{}", count_active_in_area(program.clone(), 0, 0, size));
+    }
+    if let Some(size) = opt.ship_size {
+        println!("{:?}", find_closest_ship_space(program, size))
+    }
+}
+
+fn exit_on_failed_assertion<A, E: std::error::Error>(data: Result<A, E>, message: &str) -> A {
+    match data {
+        Ok(data) => data,
+        Err(e) => {
+            eprintln!("{}: {}", message, e);
+            process::exit(1);
+        }
+    }
+}
+
+fn count_active_in_area(program: IntcodeProgram, left: usize, top: usize, size: usize) -> usize {
+    (left..left + size)
+        .flat_map(|x| (top..top + size).map(move |y| (x, y)))
+        .filter(|(x, y)| tractor_beam_is_active(program.clone(), *x, *y))
+        .count()
+}
+
+fn area_is_all_full(program: IntcodeProgram, left: usize, top: usize, size: usize) -> bool {
+    // This check with a grid that's aligned to 10 gives an early exit
+    // for most, that will have the program executions shared. This
+    // makes the memoized tractor function more effective at cutting
+    // down on execution, even though you need to do the whole lot
+    // again to verify if this passes.
+    (left..left + size)
+        .flat_map(|x| (top..top + size).map(move |y| (x, y)))
+        .filter(|(x, y)| x % 10 == 0 && y % 10 == 0)
+        .all(|(x, y)| tractor_beam_is_active(program.clone(), x, y))
+        && (left..left + size)
+            .flat_map(|x| (top..top + size).map(move |y| (x, y)))
+            .all(|(x, y)| tractor_beam_is_active(program.clone(), x, y))
+}
+
+fn find_closest_ship_space(program: IntcodeProgram, size: usize) -> (usize, usize) {
+    (0..)
+        .flat_map(|radius| {
+            (0..radius)
+                .flat_map(move |x| (0..radius).map(move |y| (x, y)))
+                .filter(move |(x, y)| {
+                    (radius - 1) * (radius - 1) < x * x + y * y && x * x + y * y <= radius * radius
+                })
+        })
+        .find(|(x, y)| area_is_all_full(program.clone(), *x, *y, size))
+        .unwrap()
+}
+
+cached_key! {
+    TRACTOR_BEAM_IS_ACTIVE: UnboundCache<(usize, usize), bool> = UnboundCache::new();
+    Key = { (x, y) };
+    fn tractor_beam_is_active(program: IntcodeProgram, x: usize, y: usize) -> bool = {
+        program
+            .with_input(list![Intcode::from(x), Intcode::from(y)])
+            .execute()
+            == Ok(vector![Intcode::from(1)])
+
+    }
+}