day 18 part 1

day18/main.swift

@@ -0,0 +1,45 @@
+import Foundation
+let input = loadData(day: 18)
+let scanner = Scanner(string: input)
+
+extension Scanner {
+    func primary() -> Int? {
+        if let num = scanInt() {
+            return num
+        }
+
+        if string("(") {
+            let result = expression()
+            if !string(")") {
+                fatalError()
+            }
+            return result
+        }
+
+        return nil
+    }
+
+    func op() -> String? {
+        scanString("+") ?? scanString("*")
+    }
+
+    func expression() -> Int? {
+        guard var result = primary() else { return nil }
+        while let op = self.op() {
+            guard let second = primary() else { fatalError() }
+            switch op {
+            case "+": result += second
+            case "*": result *= second
+            default: fatalError()
+            }
+        }
+        return result
+    }
+}
+
+var result = 0
+while let e = scanner.expression() {
+    result += e
+}
+
+print(result)