1 files changed, 169 insertions, 0 deletions
diff --git a/src/11/main.zig b/src/11/main.zig
new file mode 100644
index 0000000..857c457
--- /dev/null
+++ b/src/11/main.zig
@@ -0,0 +1,169 @@
+const std = @import("std");
+const aoc = @import("aoc");
+
+const SeatState = enum { EMPTY, FLOOR, TAKEN };
+const MapDims = struct { width: usize, height: usize };
+const Dir = struct { x: i8, y: i8 };
+const Pos = struct { x: i128, y: i128 };
+
+const adjacent = [_]Dir{
+    Dir{ .x = -1, .y = -1 },
+    Dir{ .x = -0, .y = -1 },
+    Dir{ .x = 1, .y = -1 },
+    Dir{ .x = -1, .y = 0 },
+    Dir{ .x = 1, .y = 0 },
+    Dir{ .x = -1, .y = 1 },
+    Dir{ .x = 0, .y = 1 },
+    Dir{ .x = 1, .y = 1 },
+};
+
+fn parseMap(mapitems: *[]SeatState, dims: *MapDims, input: []const u8, allocator: std.mem.Allocator) !void {
+    var lineit = std.mem.tokenize(u8, input, "\n");
+    var map = std.ArrayList(SeatState).init(allocator);
+    errdefer map.deinit();
+    while (lineit.next()) |line| {
+        if (dims.width == 0) {
+            dims.width = line.len;
+        } else if (dims.width != line.len) {
+            return aoc.Error.InvalidInput;
+        }
+        for (line) |c| {
+            try map.append(switch (c) {
+                '#' => SeatState.TAKEN,
+                'L' => SeatState.EMPTY,
+                '.' => SeatState.FLOOR,
+                else => {
+                    return aoc.Error.InvalidInput;
+                },
+            });
+        }
+        dims.height += 1;
+    }
+    mapitems.* = map.toOwnedSlice();
+}
+
+fn printMap(mapitems: []SeatState, dims: MapDims) void {
+    for (mapitems) |state, i| {
+        const c: u8 = switch (state) {
+            SeatState.EMPTY => 'L',
+            SeatState.TAKEN => '#',
+            SeatState.FLOOR => '.',
+        };
+        if (i % dims.width == 0) {
+            aoc.debugfmt("\n", .{});
+        }
+        aoc.debugfmt("{c}", .{c});
+    }
+}
+
+fn simulateStrategyOne(before: []SeatState, after: []SeatState, dims: MapDims) u32 {
+    var seat_changes: u32 = 0;
+    for (before) |state, i| {
+        const p = Pos{ .x = i % dims.width, .y = i / dims.width };
+        var count: u32 = 0;
+        for (adjacent) |ap| {
+            if (p.x + ap.x >= dims.width or p.x + ap.x < 0 or p.y + ap.y >= dims.height or p.y + ap.y < 0) continue;
+            const ni = @intCast(u64, @intCast(i64, i) + ap.x + ap.y * @intCast(i64, dims.width));
+            count += @boolToInt(before[ni] == SeatState.TAKEN);
+        }
+        if (state == SeatState.EMPTY and count == 0) {
+            after[i] = SeatState.TAKEN;
+            seat_changes += 1;
+        } else if (state == SeatState.TAKEN and count >= 4) {
+            after[i] = SeatState.EMPTY;
+            seat_changes += 1;
+        } else {
+            after[i] = before[i];
+        }
+    }
+    return seat_changes;
+}
+
+fn simulateStrategyTwo(before: []SeatState, after: []SeatState, dims: MapDims) u32 {
+    var seat_changes: u32 = 0;
+    for (before) |state, i| {
+        const p = Pos{ .x = i % dims.width, .y = i / dims.width };
+        var count: u32 = 0;
+        for (adjacent) |ap| {
+            var iterp = Pos{ .x = p.x + ap.x, .y = p.y + ap.y };
+            while (iterp.x < dims.width and iterp.x >= 0 and iterp.y < dims.height and iterp.y >= 0) {
+                const ni = @intCast(u64, iterp.x + iterp.y * @intCast(i64, dims.width));
+                if (before[ni] == SeatState.TAKEN) {
+                    count += 1;
+                    break;
+                } else if (before[ni] == SeatState.EMPTY) {
+                    break;
+                } else {
+                    iterp.x += ap.x;
+                    iterp.y += ap.y;
+                }
+            }
+        }
+        if (state == SeatState.EMPTY and count == 0) {
+            after[i] = SeatState.TAKEN;
+            seat_changes += 1;
+        } else if (state == SeatState.TAKEN and count >= 5) {
+            after[i] = SeatState.EMPTY;
+            seat_changes += 1;
+        } else {
+            after[i] = before[i];
+        }
+    }
+    return seat_changes;
+}
+
+fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var mapdims = MapDims{ .width = 0, .height = 0 };
+    var mapitems: []SeatState = undefined;
+    try parseMap(&mapitems, &mapdims, input, allocator);
+    defer allocator.free(mapitems);
+
+    var mapresult = try allocator.alloc(SeatState, mapitems.len);
+    defer allocator.free(mapresult);
+
+    var round: u32 = 0;
+    while (simulateStrategyOne(mapitems, mapresult, mapdims) > 0) : (round += 1) {
+        aoc.debugfmt("\rRound: {}", .{round});
+        std.mem.copy(SeatState, mapitems, mapresult);
+    }
+
+    var taken_count: u64 = 0;
+    for (mapresult) |state| {
+        taken_count += @boolToInt(state == SeatState.TAKEN);
+    }
+
+    aoc.debugfmt("\nSeats Occupied: {}\n", .{taken_count});
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{taken_count});
+}
+
+fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
+    _ = args;
+
+    var mapdims = MapDims{ .width = 0, .height = 0 };
+    var mapitems: []SeatState = undefined;
+    try parseMap(&mapitems, &mapdims, input, allocator);
+    defer allocator.free(mapitems);
+
+    var mapresult = try allocator.alloc(SeatState, mapitems.len);
+    defer allocator.free(mapresult);
+
+    var round: u32 = 0;
+    while (simulateStrategyTwo(mapitems, mapresult, mapdims) > 0) : (round += 1) {
+        aoc.debugfmt("\rRound: {}", .{round});
+        std.mem.copy(SeatState, mapitems, mapresult);
+    }
+
+    var taken_count: u64 = 0;
+    for (mapresult) |state| {
+        taken_count += @boolToInt(state == SeatState.TAKEN);
+    }
+
+    aoc.debugfmt("\nSeats Occupied: {}\n", .{taken_count});
+
+    return try std.fmt.allocPrint(allocator, "{d}", .{taken_count});
+}
+
+pub const main = aoc.main(part1, part2, .{ "2126", "1914" });