From 1b09653fccbcec00492c78026dd5062c669714b6 Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Fri, 11 Dec 2020 19:24:09 +0100
Subject: [PATCH] Day 11 (ugly)

---
 2020/day11.py | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2020/grid.py  | 47 +++++++++++++++++++++++----------
 2 files changed, 106 insertions(+), 14 deletions(-)
 create mode 100644 2020/day11.py

diff --git a/2020/day11.py b/2020/day11.py
new file mode 100644
index 0000000..6ff85aa
--- /dev/null
+++ b/2020/day11.py
@@ -0,0 +1,73 @@
+import sys
+
+from grid import Grid, near8
+
+
+def main():
+    lines = [line.rstrip() for line in sys.stdin]
+
+    # Part 1
+    g = Grid(value_factory=lambda: ".", lines=lines)
+    while update(g):
+        pass
+    print("Occupied:", sum(v == "#" for _, _, v in g.values_gen()))
+
+    # Part 2
+    g = Grid(value_factory=lambda: ".", lines=lines)
+    while update2(g):
+        pass
+    print("Occupied part 2:", sum(v == "#" for _, _, v in g.values_gen()))
+
+
+def update(g):
+    changes = {}
+    for x, y, v in g.values_gen():
+        if v == ".":
+            continue
+        p = (x, y)
+        n = list(g.near_objects(p, near_f=near8).values())
+        if v == "L" and n.count("#") == 0:
+            changes[p] = "#"
+        elif v == "#" and n.count("#") >= 4:
+            changes[p] = "L"
+    for (x, y), v in changes.items():
+        g.setv(x, y, v)
+    return bool(changes)
+
+
+RAYS_OFS = [
+    (-1, -1), ( 0, -1), ( 1, -1),
+    (-1,  0),           ( 1,  0),
+    (-1,  1), ( 0,  1), ( 1,  1),
+]
+
+
+def update2(g):
+    changes = {}
+    for x, y, v in g.values_gen():
+        if v == ".":
+            continue
+        occ = 0 
+        for ox, oy in RAYS_OFS:
+            n = 1
+            while True:
+                qx, qy = x + ox * n, y + oy * n
+                if not g.hasv(qx, qy):
+                    break
+                if (rv := g.getv(qx, qy)) == "#":
+                    occ += 1
+                    break
+                elif rv == "L":
+                    break
+                n += 1
+        if v == "L" and occ == 0:
+            changes[(x, y)] = "#"
+        elif v == "#" and occ >= 5:
+            changes[(x, y)] = "L"
+    for (x, y), v in changes.items():
+        g.setv(x, y, v)
+    return bool(changes)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/2020/grid.py b/2020/grid.py
index 87d7829..d37350c 100644
--- a/2020/grid.py
+++ b/2020/grid.py
@@ -3,6 +3,30 @@
 from collections import defaultdict
 
 
+def near(p):
+    """Return a tuple of neighbor positions (up, left, down, right)."""
+    return (
+        (p[0]    , p[1] - 1),
+        (p[0] + 1, p[1]    ),
+        (p[0]    , p[1] + 1),
+        (p[0] - 1, p[1]    ),
+    )
+
+
+def near8(p):
+    """Return a tuple of neighbor positions, including diagonals."""
+    return (
+        (p[0] - 1, p[1] - 1),
+        (p[0]    , p[1] - 1),
+        (p[0] + 1, p[1] - 1),
+        (p[0] - 1, p[1]    ),
+        (p[0] + 1, p[1]    ),
+        (p[0] - 1, p[1] + 1),
+        (p[0]    , p[1] + 1),
+        (p[0] + 1, p[1] + 1),
+    )
+
+
 class Grid:
 
     def __init__(self, value_factory=int, lines=None):
@@ -10,6 +34,9 @@ class Grid:
         if lines:
             self.load(lines)
 
+    def hasv(self, x, y):
+        return y in self.g and x in self.g[y]
+
     def getv(self, x, y):
         return self.g[y][x]
 
@@ -26,9 +53,12 @@ class Grid:
             for x, v in row.items():
                 yield (x, y, v)
 
-    def near_objects(self, p):
-        """Return a dict of neighbor positions to values (U, L, D, R)."""
-        return {q: self.g[q[1]][q[0]] for q in Grid.near(p)}
+    def near_objects(self, p, near_f=near):
+        return {
+            q: self.getv(q[0], q[1])
+            for q in near_f(p)
+            if self.hasv(q[0], q[1])  # do not create entries.
+        }
 
     def dumb_print(self, f=lambda v: v):
         for row in self.g.values():
@@ -37,19 +67,8 @@ class Grid:
             print()
 
     def print_near(self, p, view_size=2):
-        """Print near values in an area of view_size. Works iff keys support addition."""
         for dy in range(-view_size, view_size + 1):
             print("".join([
                 self.g[p[1] + dy][p[0] + dx]
                 for dx in range(-view_size, view_size + 1)
             ]))
-
-    @staticmethod
-    def near(p):
-        """Return a tuple of neighbor positions (up, left, down, right)."""
-        return (
-            (p[0]    , p[1] - 1),
-            (p[0] + 1, p[1]    ),
-            (p[0]    , p[1] + 1),
-            (p[0] - 1, p[1]    ),
-        )