add: miracously did this on mobile while skiing

2025/06/p1.rs

@@ -0,0 +1,40 @@
+#[derive(Clone, Copy, Debug)]
+enum Op {
+    Mul,
+    Add,
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "Rust" fn challenge_usize(buf: &[u8]) -> usize {
+    use Op::*;
+
+    let mut iter = buf[0..(buf.len() - 1)].rsplit(|&b| b == b'\n').map(|ln| {
+        unsafe { str::from_utf8_unchecked(ln) }
+            .split(' ')
+            .map(|e| e.trim())
+            .filter(|e| !e.is_empty())
+    });
+
+    let mut ops = iter
+        .next()
+        .unwrap()
+        .map(|op| match op {
+            "*" => (Mul, 1),
+            "+" => (Add, 0),
+            _ => unreachable!("invalid op"),
+        })
+        .collect::<Vec<_>>();
+
+    iter.for_each(|ln| {
+        ln.zip(ops.iter_mut()).for_each(|(n, acc)| {
+            let n: usize = n.parse().unwrap();
+
+            match acc.0 {
+                Mul => acc.1 *= n,
+                Add => acc.1 += n,
+            }
+        });
+    });
+
+    ops.iter().fold(0, |acc, (_, n)| acc + n)
+}