1 files changed, 67 insertions, 0 deletions
diff --git a/src/08/main.zig b/src/08/main.zig
new file mode 100644
index 0000000..d8aa00f
--- /dev/null
+++ b/src/08/main.zig
@@ -0,0 +1,67 @@
+const std = @import("std");
+const aoc = @import("aoc");
+const Console = @import("console8").Console;
+
+fn runTillRepeat(console: *Console, instlist: *std.ArrayList(u64), swapon: ?u64) !void {
+    while (try console.parseNext()) |_inst| {
+        var inst = _inst;
+        aoc.debugfmt("{:<5}: {s} {d}\n", .{ console.instructptr, inst.opcode, inst.argval });
+        if (std.mem.indexOfScalar(u64, instlist.items, console.instructptr) != null) {
+            return;
+        }
+        if (swapon != null and swapon.? == console.instructptr) {
+            inst.opfunc = switch (inst.opfunc) {
+                Console.jumpInstruction => Console.nopInstruction,
+                Console.nopInstruction => Console.jumpInstruction,
+                else => unreachable,
+            };
+        }
+        try instlist.append(console.instructptr);
+        try console.exec(&inst);
+    }
+}
+
+fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var console = try Console.init(input, allocator);
+    defer console.deinit();
+
+    var instlist = std.ArrayList(u64).init(allocator);
+    defer instlist.deinit();
+
+    try runTillRepeat(&console, &instlist, null);
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{console.accumulator});
+}
+
+fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var console = try Console.init(input, allocator);
+    defer console.deinit();
+
+    var instlist = std.ArrayList(u64).init(allocator);
+    defer instlist.deinit();
+
+    try runTillRepeat(&console, &instlist, null);
+
+    for (instlist.items) |inst| {
+        if (std.mem.eql(u8, "acc"[0..3], console.instlist[inst][0..3]))
+            continue;
+
+        var sim_seen = std.ArrayList(u64).init(allocator);
+        defer sim_seen.deinit();
+
+        console.reset();
+        //std.debug.print("Swapping instruction: {:<5}: {}\n", .{ inst, console.instlist[inst] });
+        runTillRepeat(&console, &sim_seen, inst) catch {};
+        if (console.jumpAddr == console.instlist.len or console.instructptr == console.instlist.len) {
+            return try std.fmt.allocPrint(allocator, "{d}", .{console.accumulator});
+        }
+    }
+
+    return null;
+}
+
+pub const main = aoc.main(part1, part2, .{ "1766", "1639" });