remove string methods

day01/Sources/day01/day01.swift

@@ -3,14 +3,15 @@
 
 @main
 struct day01 {
-    static func parseInput(_ input: String) -> [(Direction, Int)] {
-        return input.split(whereSeparator: {char in char.isNewline})
-        .map({ line in
-            return (Direction(line.first!), Int(line.dropFirst())!)
+    static func parseInput(_ input: [StaticString]) -> [(Direction, Int)] {
+        input.map({ line in
+            let turns = line.withUTF8Buffer { tmp in
+                atoi(str: [UInt8](tmp.dropFirst()))
+            }
+            return (Direction(line.utf8Start[0]), turns)
         })
     }
 
-
     static func part1(_ input: [(Direction, Int)]) {
         var cur = 50
         var count = 0
@@ -59,16 +60,30 @@ struct day01 {
         part1(parsed)
         part2(parsed)
     }
+
+    static func atoi(str: [UInt8]) -> Int {
+        var result = 0
+
+        for char in str {
+            if char >= 0x30 && char <= 0x39 {
+                result = result * 10 + (Int(char) - 0x30)
+            } else {
+                break
+            }
+        }
+
+        return result
+    }
 }
 
 enum Direction {
     case Left
     case Right
 
-    init(_ char: Character) {
+    init(_ char: UInt8) {
         self = switch char {
-            case "L": Direction.Left
-            case "R": Direction.Right
+            case 0x4c: Direction.Left
+            case 0x52: Direction.Right
             default: fatalError()
         }
     }