Solution to problem 11 part 2

src/P11.py

@@ -172,5 +172,196 @@ def part_1(seats: list[str]) -> None:
     print(f"There are {free_seats(seats)} seats occupied")
 
 
+# --- Part Two ---
+
+# As soon as people start to arrive, you realize your mistake. People don't
+# just care about adjacent seats - they care about the first seat they can see
+# in each of those eight directions!
+
+# Now, instead of considering just the eight immediately adjacent seats,
+# consider the first seat in each of those eight directions. For example, the
+# empty seat below would see eight occupied seats:
+
+# .......#.
+# ...#.....
+# .#.......
+# .........
+# ..#L....#
+# ....#....
+# .........
+# #........
+# ...#.....
+
+# The leftmost empty seat below would only see one empty seat, but cannot see
+# any of the occupied ones:
+
+# .............
+# .L.L.#.#.#.#.
+# .............
+
+# The empty seat below would see no occupied seats:
+
+# .##.##.
+# #.#.#.#
+# ##...##
+# ...L...
+# ##...##
+# #.#.#.#
+# .##.##.
+
+# Also, people seem to be more tolerant than you expected: it now takes five or
+# more visible occupied seats for an occupied seat to become empty (rather than
+# four or more from the previous rules). The other rules still apply: empty
+# seats that see no occupied seats become occupied, seats matching no rule
+# don't change, and floor never changes.
+
+# Given the same starting layout as above, these new rules cause the seating
+# area to shift around as follows:
+
+# 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
+
+# #.##.##.##
+# #######.##
+# #.#.#..#..
+# ####.##.##
+# #.##.##.##
+# #.#####.##
+# ..#.#.....
+# ##########
+# #.######.#
+# #.#####.##
+
+# #.LL.LL.L#
+# #LLLLLL.LL
+# L.L.L..L..
+# LLLL.LL.LL
+# L.LL.LL.LL
+# L.LLLLL.LL
+# ..L.L.....
+# LLLLLLLLL#
+# #.LLLLLL.L
+# #.LLLLL.L#
+
+# #.L#.##.L#
+# #L#####.LL
+# L.#.#..#..
+# ##L#.##.##
+# #.##.#L.##
+# #.#####.#L
+# ..#.#.....
+# LLL####LL#
+# #.L#####.L
+# #.L####.L#
+
+# #.L#.L#.L#
+# #LLLLLL.LL
+# L.L.L..#..
+# ##LL.LL.L#
+# L.LL.LL.L#
+# #.LLLLL.LL
+# ..L.L.....
+# LLLLLLLLL#
+# #.LLLLL#.L
+# #.L#LL#.L#
+
+# #.L#.L#.L#
+# #LLLLLL.LL
+# L.L.L..#..
+# ##L#.#L.L#
+# L.L#.#L.L#
+# #.L####.LL
+# ..#.#.....
+# LLL###LLL#
+# #.LLLLL#.L
+# #.L#LL#.L#
+
+# #.L#.L#.L#
+# #LLLLLL.LL
+# L.L.L..#..
+# ##L#.#L.L#
+# L.L#.LL.L#
+# #.LLLL#.LL
+# ..#.L.....
+# LLL###LLL#
+# #.LLLLL#.L
+# #.L#LL#.L#
+
+# Again, at this point, people stop shifting around and the seating area
+# reaches equilibrium. Once this occurs, you count 26 occupied seats.
+
+# Given the new visibility method and the rule change for occupied seats
+# becoming empty, once equilibrium is reached, how many seats end up occupied?
+
+
+def seats_around_mod(seats: list[str], r: int, c: int) -> int:
+    total = 0
+    around_me = [
+        (-1, -1),
+        (-1, 0),
+        (-1, 1),
+        (0, -1),
+        (0, 1),
+        (1, -1),
+        (1, 0),
+        (1, 1),
+    ]
+    for row, col in around_me:
+        _row = r + row
+        _col = c + col
+        while (
+            _row >= 0
+            and _row < len(seats)
+            and _col < len(seats[c])
+            and seats[_row][_col] == "."
+        ):
+            _row += row
+            _col += col
+        if (
+            _row >= 0
+            and _row < len(seats)
+            and _col >= 0
+            and _col < len(seats[c])
+        ):
+            total += seats[_row][_col] == "#"
+    return total
+
+
+def part_2(seats: list[str]) -> None:
+    R = len(seats)
+    C = len(seats[0])
+    while True:
+        has_changed = False
+        next_iter = []
+        for r in range(R):
+            new_row = ""
+            for c in range(C):
+                seat = seats[r][c]
+                if seat != ".":
+                    occupants = seats_around_mod(seats, r, c)
+                    if seat == "L" and occupants == 0:
+                        seat = "#"
+                        has_changed = True
+                    elif seat == "#" and occupants >= 5:
+                        seat = "L"
+                        has_changed = True
+                new_row += seat
+            next_iter.append(new_row)
+        if not has_changed:
+            break
+        seats = next_iter
+
+    print(f"There are {free_seats(seats)} seats occupied")
+
+
 if __name__ == "__main__":
     part_1(seats)
+    part_2(seats)