123 lines
2.6 KiB
Python
123 lines
2.6 KiB
Python
import itertools
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rocks = [
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0b00011110,
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0b00001000_00011100_00001000,
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0b00000100_00000100_00011100,
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0b00010000_00010000_00010000_00010000,
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0b00011000_00011000,
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]
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wall = 0b10000000_10000000_10000000_10000000_10000000
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jets = ">>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>"
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jets = open("input").read().strip()
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def ceil(n):
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if n%8 != 0:
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n += 8 - n%8
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return n
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def drop(a, r, jets):
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h = ceil(a.bit_length()) + 8*3
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numjets = 0
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while True:
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# push left or right
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j = next(jets)
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if j == '<':
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x = (r<<1)
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if x & wall == 0:
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if x & (a>>h) == 0:
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r = x
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elif j == '>':
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x = (r<<7)
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if x & wall == 0:
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x >>= 8
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if x & (a>>h) == 0:
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r = x
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numjets += 1
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# continue falling?
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if r & (a>>(h-8)) == 0:
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h -= 8
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assert h > 0
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else:
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# stop
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a |= (r<<h)
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return a, numjets
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def head(a):
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# technically this isn't sufficient.
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# you could imagine a stack of overhangs like
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#
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# |# #|
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# |#### #|
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# |# #|
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# |# #|
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# |# ###|
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# |# #|
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#
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# that a rock might be able to navigate through indefinitely,
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# but our stacks are much messier than that, so no need to worry.
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#
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# we could probably just take the top 10 or so rows and call it good.
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h = ceil(a.bit_length())
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x = 0x80
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while h >= 8:
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h -= 8
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x |= (a>>h)&0xff
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if x == 0xff:
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return a>>h
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return a
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def height(a):
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return ceil(a.bit_length())//8
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# Part 1
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a = 0b11111111
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jeti = itertools.cycle(jets)
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rocki = itertools.cycle(rocks)
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for _ in range(2022):
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r = next(rocki)
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a, _ = drop(a,r,jeti)
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print(height(a>>8))
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# Part 2
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a = 0b11111111
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stopped = 0
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jeti = itertools.cycle(jets)
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rocki = itertools.cycle(rocks)
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i = 0
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j = 0
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seen = dict()
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try:
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while True:
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r = next(rocki)
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a, n = drop(a,r,jeti)
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stopped += 1
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i = (i+1) % len(rocks)
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j = (j+n) % len(jets)
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if (i,j,head(a)) in seen:
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break
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seen[(i,j,head(a))] = (a,stopped)
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#for i in reversed(range(0,a.bit_length(),8)):
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# print("{:08b}".format((a>>i)&0xff))
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#print()
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except:
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print(i, j, stopped)
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raise
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b, old = seen[(i,j,head(a))]
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sdiff = stopped - old
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hdiff = height(a) - height(b)
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goal = 10**12
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rounds, extra = divmod(goal - stopped, sdiff)
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for _ in range(extra):
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r = next(rocki)
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a, n = drop(a,r,jeti)
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print(rounds*hdiff + height(a)-1)
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