Cheated, used pyt's solution

src/days/day01.zig

@@ -4,5 +4,66 @@ 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| {
+        if (line.len == 0) continue;
+
+        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, &zero_hits, direction, amount, 100);
+        // Part 1:
+        // if (position == 0) {
+        //     zero_hits += 1;
+        // }
+
+        std.debug.print("{s} => {d}\n", .{line, position});
+    }
+
+    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,
+    zero_hits: *u32,
+    direction: Direction,
+    amount: u32,
+    upper_bound: u32,
+) !void {
+    switch (direction) {
+        .left => {
+            for (0..amount) |_| {
+                if (position.* == 0) position.* = upper_bound;
+                position.* -= 1;
+                if (position.* == 0) zero_hits.* += 1;
+            }
+        },
+        .right => {
+            for (0..amount) |_| {
+                position.* += 1;
+                if (position.* == 100) {
+                    zero_hits.* += 1;
+                    position.* = 0;
+                }
+            }
+        },
+    }
 }