refact: day 19 part 1 with linked lists

day19/src/main.rs

@@ -4,39 +4,29 @@ const LENGTH: usize = 5;
 const LENGTH: usize = 3_017_957;
 
 fn main() {
-    let mut pointer = 0;
-    let mut has_presents = [true; LENGTH];
-    let mut next_elf = [0; LENGTH];
+    let builder = std::thread::Builder::new().stack_size(100_000_000);
+    let handle = builder.spawn(part_1).unwrap();
+    handle.join().unwrap();
+}
 
-    for (idx, val) in next_elf.iter_mut().enumerate() {
+fn part_1() {
+    let mut pointer = 0;
+
+    let mut next = [0; LENGTH];
+
+    for (idx, val) in next.iter_mut().enumerate() {
         *val = (idx + 1) % LENGTH;
     }
 
-    'outer: loop {
-        let mut offset = 1;
-        loop {
-            let idx = (pointer + offset) % LENGTH;
-            if has_presents[idx] {
-                has_presents[idx] = false;
-                pointer = idx;
-                break;
-            } else {
-                offset += 1;
-            }
-        }
-        let count = has_presents.iter().filter(|b| **b).count();
-        println!("{count}");
-        if count == 1 {
-            let correct_idx = has_presents
-                .iter()
-                .enumerate()
-                .filter(|(_, b)| **b)
-                .map(|(i, _)| i)
-                .next()
-                .unwrap()
-                + 1;
-            println!("{correct_idx}");
-            break 'outer;
+    loop {
+        next[pointer] = next[next[pointer]];
+
+        pointer = next[pointer];
+
+        // only one elf left
+        if next[pointer] == pointer {
+            println!("{}", pointer + 1);
+            break;
         }
     }
 }