day 23, animate elves' spreading

d23/paint.py

@@ -0,0 +1,69 @@
+import sys
+
+E = { (y,x) for y,l in enumerate(sys.stdin.read().splitlines())
+	for x,c in enumerate(l)
+		if c == '#' }
+
+def can(y,x):
+	can1 = (y-1,x-1) not in E
+	can2 = (y-1,x) not in E
+	can3 = (y-1,x+1) not in E
+	can4 = (y,x+1) not in E
+	can5 = (y+1,x+1) not in E
+	can6 = (y+1,x) not in E
+	can7 = (y+1,x-1) not in E
+	can8 = (y,x-1) not in E
+	return [can1,can2,can3,can4,can5,can6,can7,can8]
+
+def canN(y,x,can1,can2,can3,can4,can5,can6,can7,can8):
+	if can1 and can2 and can3:
+		return (y-1,x)
+def canS(y,x,can1,can2,can3,can4,can5,can6,can7,can8):
+	if can5 and can6 and can7:
+		return (y+1,x)
+def canW(y,x,can1,can2,can3,can4,can5,can6,can7,can8):
+	if can7 and can8 and can1:
+		return (y,x-1)
+def canE(y,x,can1,can2,can3,can4,can5,can6,can7,can8):
+	if can3 and can4 and can5:
+		return (y,x+1)
+
+def draw(r):
+	with open(f"./pics/{r:05d}.pbm","wt") as f:
+		(minx,maxx,miny,maxy) = (-13,129,-13,129)
+		w = 4*(maxx -minx +1)
+		print("P1",file=f)
+		print(f"{w} {w}", file=f)
+		for y in range(miny,maxy+1):
+			a="".join(["0000","1111"][(y,x) in E] for x in range(minx,maxx+1))
+			print(a,file=f)
+			print(a,file=f)
+			print(a,file=f)
+			print(a,file=f)
+
+from collections import deque
+dirs = deque([canN,canS,canW,canE])
+for r in range(int(sys.argv[1])):  # rounds
+	P = dict()  # { new_pos: old_pos }
+	for e in E:  # for each elve
+		(y,x) = e
+		cans = can(y,x)  # compute once instead of four
+		moves = [ d(y,x,*cans) for d in dirs ]
+		if all(m is not None for m in moves):  # far away
+			continue
+		if all(m is None for m in moves):  # all packed
+			continue
+		p = next(filter(lambda m: m is not None ,moves))
+		if p not in P: # can move
+			P[p] = (y,x)
+		else: # occupied, invalidate move for all
+			P[p] = None
+	moved = { v for k,v in P.items() if v is not None }
+	newpos = { k for k,v in P.items() if v is not None }
+	if len(newpos) == 0:
+		break
+	if r % 11 == 0:
+		draw(r)
+	E = (E - moved) | newpos
+	dirs.rotate(-1)
+# then, $TIME convert -delay 25 -loop 0 pics/* a.gif