day 18 part 2 faster with binary search

src/day18.rs

@@ -69,12 +69,34 @@ fn part2(input: &str) -> String {
 
 fn solve2(input: &str, fixed: usize, max_coord: i32) -> String {
     let points = parse(input);
-    for i in fixed..points.len() {
-        if let None = sp(&points[..=i], max_coord) {
-            return format!("{},{}", points[i].0, points[i].1);
+
+    // we want the first point with which there is no shortest path
+    let mut i = fixed;
+    let mut jump = (points.len() - fixed) / 2;
+    #[cfg(debug_assertions)]
+    let mut loops = 0;
+    loop {
+        #[cfg(debug_assertions)]
+        {
+            loops += 1;
+        }
+        let l = sp(&points[..i - 1], max_coord);
+        let r = sp(&points[..i], max_coord);
+        if l.is_some() && r.is_none() {
+            #[cfg(debug_assertions)]
+            dbg!(loops);
+            return format!("{},{}", points[i - 1].0, points[i - 1].1);
+        }
+        if l.is_some() {
+            i += jump;
+        } else {
+            i -= jump;
+        }
+        jump /= 2;
+        if jump == 0 {
+            jump += 1;
         }
     }
-    unreachable!()
 }
 
 #[cfg(test)]

src/main.rs

@@ -22,6 +22,7 @@ fn main() {
         (15, day15::day_main),
         (16, day16::day_main),
         (17, day17::day_main),
+        (18, day18::day_main),
         (19, day19::day_main),
         (21, day21::day_main),
         (22, day22::day_main),
@@ -29,17 +30,20 @@ fn main() {
         (23, day23::day_main),
         (24, day24::day_main),
         (25, day25::day_main),
-        (18, day18::day_main),
         // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());
     let Some(day) = day else {
+        let start = Instant::now();
         mains
             .iter()
             .sorted_by_key(|entry| entry.0)
             .for_each(|(d, f)| {
                 run(*d, f);
             });
+        let duration = start.elapsed();
+        println!();
+        println!("{COLOR}{ITALIC}All tasks took {duration:?}{RESET_FORMATTING}");
         return;
     };