add day 19 naive approach

day19/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day19"
+version = "0.1.0"

day19/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "day19"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+
+[profile.release]
+lto = "fat"

day19/src/main.rs

@@ -0,0 +1,42 @@
+#[cfg(debug_assertions)]
+const LENGTH: usize = 5;
+#[cfg(not(debug_assertions))]
+const LENGTH: usize = 3_017_957;
+
+fn main() {
+    let mut pointer = 0;
+    let mut has_presents = [true; LENGTH];
+    let mut next_elf = [0; LENGTH];
+
+    for (idx, val) in next_elf.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;
+        }
+    }
+}