WIP: implement day 1

src/days/day01.zig

@@ -4,5 +4,62 @@ pub const title = "Day 01: Secret Entrance";
 
 pub fn run(_: std.mem.Allocator) !void {
     const input = @embedFile("./input/day01.txt");
+    var lines = std.mem.tokenizeScalar(u8, input, '\n');
+
+    const starting_position = 50;
+    var position: u32 = starting_position;
+
+    var zero_hits: u32 = 0;
+
+    while (lines.next()) |line| {
+        const direction: Direction = if (line[0] == 'L') .left else if (line[0] == 'R') .right else continue;
+        const amount = try std.fmt.parseUnsigned(u32, line[1..], 10);
+        try updatePosition(&position, direction, amount, 99);
+        if (position == 0) {
+            zero_hits += 1;
+        }
+    }
+
+    var buffer: [8]u8 = undefined;
+    var stdout_writer = std.fs.File.stdout().writer(&buffer);
+    const stdout = &stdout_writer.interface;
+
+    try stdout.print("{d}\n", .{zero_hits});
+
+    try stdout.flush();
+}
+
+const Direction = enum {
+    left,
+    right,
+};
+
+fn updatePosition(
+    position: *u32,
+    direction: Direction,
+    amount: u32,
+    upper_bound: u32,
+) !void {
+    var signed_position: i32 = @intCast(position.*);
+
+    switch (direction) {
+        .left => {
+            signed_position -= @intCast(amount);
+        },
+        .right => {
+            signed_position += @intCast(amount);
+        },
+    }
+
+    if (signed_position == upper_bound) {
+        position.* = @intCast(signed_position);
+    } else if (signed_position == 0) {
+        position.* = 0;
+    } else if (signed_position > upper_bound or signed_position < 0) {
+        const signed_upper_bound: i32 = @intCast(upper_bound);
+        var mod = @mod(signed_position, signed_upper_bound);
+        if (signed_position < 0) mod += 1;
+        position.* = @intCast(mod);
+    }
 }