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+--- Day 11: Seating System ---
+
+Your plane lands with plenty of time to spare. The final leg of your journey is a ferry that goes
+directly to the tropical island where you can finally start your vacation. As you reach the waiting
+area to board the ferry, you realize you're so early, nobody else has even arrived yet!
+
+By modeling the process people use to choose (or abandon) their seat in the waiting area, you're
+pretty sure you can predict the best place to sit. You make a quick map of the seat layout (your
+puzzle input).
+
+The seat layout fits neatly on a grid. Each position is either floor (.), an empty seat (L), or an
+occupied seat (#). For example, the initial seat layout might look like this:
+
+L.LL.LL.LL LLLLLLL.LL L.L.L..L.. LLLL.LL.LL L.LL.LL.LL L.LLLLL.LL ..L.L..... LLLLLLLLLL L.LLLLLL.L
+L.LLLLL.LL
+
+Now, you just need to model the people who will be arriving shortly. Fortunately, people are
+entirely predictable and always follow a simple set of rules. All decisions are based on the
+number of occupied seats adjacent to a given seat (one of the eight positions
+immediately up, down, left, right, or diagonal from the seat). The following rules are applied to
+every seat simultaneously:
+
+- If a seat is empty (L) and there are no occupied seats adjacent to it,
+the seat becomes occupied. - If a seat is occupied (#) and four
+or more seats adjacent to it are also occupied, the seat becomes empty. -
+Otherwise, the seat's state does not change.
+
+Floor (.) never changes; seats don't move, and nobody sits on the floor.
+
+After one round of these rules, every seat in the example layout becomes occupied:
+
+#.##.##.## #######.## #.#.#..#.. ####.##.## #.##.##.## #.#####.## ..#.#..... ########## #.######.#
+#.#####.##
+
+After a second round, the seats with four or more occupied adjacent seats become empty again:
+
+#.LL.L#.## #LLLLLL.L# L.L.L..L.. #LLL.LL.L# #.LL.LL.LL #.LLLL#.## ..L.L..... #LLLLLLLL# #.LLLLLL.L
+#.#LLLL.##
+
+This process continues for three more rounds:
+
+#.##.L#.## #L###LL.L# L.#.#..#.. #L##.##.L# #.##.LL.LL #.###L#.## ..#.#..... #L######L# #.LL###L.L
+#.#L###.##
+
+#.#L.L#.## #LLL#LL.L# L.L.L..#.. #LLL.##.L# #.LL.LL.LL #.LL#L#.## ..L.L..... #L#LLLL#L# #.LLLLLL.L
+#.#L#L#.##
+
+#.#L.L#.## #LLL#LL.L# L.#.L..#.. #L##.##.L# #.#L.LL.LL #.#L#L#.## ..L.L..... #L#L##L#L# #.LLLLLL.L
+#.#L#L#.##
+
+At this point, something interesting happens: the chaos stabilizes and further applications of these
+rules cause no seats to change state! Once people stop moving around, you count 37
+occupied seats.
+
+Simulate your seating area by applying the seating rules repeatedly until no seats change state.
+How many seats end up occupied?
+
+