Multithread it

src/bin/d15p2.rs

@@ -1,12 +1,44 @@
+use std::{
+    sync::{Arc, Mutex},
+    thread,
+};
+
 use aoc22::{day15, util};
 use itertools::Itertools;
 
 const COORD_MAX: isize = 4000000;
+const NUM_THREADS: usize = 16;
 
 pub fn main() {
-    let sensors = day15::parse_sensors(&util::parse_input());
+    let sensors = Arc::new(day15::parse_sensors(&util::parse_input()));
+
+    let mut handles = vec![];
+    let next_row = Arc::new(Mutex::new(0));
+
+    for _ in 0..NUM_THREADS {
+        let sensors = sensors.clone();
+        let next_row = next_row.clone();
+        let handle = thread::spawn(move || find_possible(&sensors, next_row));
+        handles.push(handle);
+    }
+
+    for handle in handles {
+        handle.join().unwrap();
+    }
+}
+
+pub fn find_possible(sensors: &Vec<day15::Sensor>, next_row: Arc<Mutex<isize>>) {
+    loop {
+        let row = {
+            let mut handle = next_row.lock().unwrap();
+            let result = *handle;
+            if result > COORD_MAX {
+                return;
+            }
+            *handle += 1;
+            result
+        };
 
-    for row in 0..=COORD_MAX {
         let covered = sensors
             .iter()
             .map(|s| s.covered(row))
@@ -25,7 +57,12 @@ pub fn main() {
                     x * 4000000 + row
                 )
             } else if max_x != isize::MIN && min > max_x + 2 {
-                panic!("More than one coordinate free: {}..{}", max_x + 1, min - 1);
+                panic!(
+                    "More than one coordinate free in row {}: {}..{}",
+                    row,
+                    max_x + 1,
+                    min - 1
+                );
             }
             max_x = max_x.max(max);
         }