day 11

1 files changed, 123 insertions, 0 deletions

diff --git a/20/py/d11.py b/20/py/d11.py
new file mode 100644
index 0000000..5d5e0c5
--- /dev/null
+++ b/20/py/d11.py
@@ -0,0 +1,123 @@
+#!/usr/bin/env python3
+import aoc20
+import sys
+
+
+def vis(board, w, h):
+    s = ""
+    for y in range(h):
+        for x in range(w):
+            p = (x, y)
+            if p in board:
+                if board[p] == -1:
+                    s += "."
+                elif board[p] == 0:
+                    s += "L"
+                elif board[p] == 1:
+                    s += "#"
+                else:
+                    s += "?"
+            else:
+                s += "?"
+        s += "\n"
+    return s
+
+
+def amount_neighbours_occ(p, board):
+    amount = 0
+    for dy in range(-1, 1+1):
+        for dx in range(-1, 1+1):
+            if dy == dx == 0:
+                continue
+            new_p = (p[0] + dx, p[1] + dy)
+            if new_p in board and board[new_p] == 1:
+                amount += 1
+    return amount
+
+
+def pt1(_in):
+    board = {}
+    h = len(_in)
+    w = len(_in[0])
+    for y in range(h):
+        for x in range(w):
+            if _in[y][x] == "L":
+                board[(x, y)] = 0
+            elif _in[y][x] == ".":
+                board[(x, y)] = -1
+
+    while True:
+        prev_board = board.copy()
+        for p, state in prev_board.items():
+            if state == 0:
+                # empty
+                if amount_neighbours_occ(p, prev_board) == 0:
+                    board[p] = 1
+            if state == 1:
+                # occ
+                if amount_neighbours_occ(p, prev_board) >= 4:
+                    board[p] = 0
+        if prev_board == board:
+            break
+        prev_board = board
+    res = 0
+    for _, state in board.items():
+        if state == 1:
+            res += 1
+    return res
+
+
+def amount_in_sight_occ(p, board, w, h):
+    amount = 0
+    dirs = ((1, 0), (1, 1), (0, 1), (-1, 1), (-1, 0), (-1, -1), (0, -1), (1, -1))
+    for dir in dirs:
+        step = 0
+        while True:
+            step += 1
+            new_p = p[0] + dir[0] * step, p[1] + dir[1] * step
+            if new_p not in board:
+                break
+            if board[new_p] == -1:
+                continue
+            if board[new_p] == 1:
+                amount += 1
+            break
+    return amount
+
+
+def pt2(_in):
+    board = {}
+    h = len(_in)
+    w = len(_in[0])
+    for y in range(h):
+        for x in range(w):
+            if _in[y][x] == "L":
+                board[(x, y)] = 0
+            elif _in[y][x] == ".":
+                board[(x, y)] = -1
+
+    while True:
+        prev_board = board.copy()
+        for p, state in prev_board.items():
+            if state == 0:
+                # empty
+                if amount_in_sight_occ(p, prev_board, w, h) == 0:
+                    board[p] = 1
+            if state == 1:
+                # occ
+                if amount_in_sight_occ(p, prev_board, w, h) >= 5:
+                    board[p] = 0
+        if prev_board == board:
+            break
+        prev_board = board
+    res = 0
+    for _, state in board.items():
+        if state == 1:
+            res += 1
+    return res
+
+
+if __name__ == "__main__":
+    input = aoc20.read_input(sys.argv[1:], 11)
+    print(pt1(input))
+    print(pt2(input))