110 lines
3.0 KiB
Python
110 lines
3.0 KiB
Python
from lib import *
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from math import lcm
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from collections import deque
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EXAMPLE = """
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broadcaster -> a, b, c
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%a -> b
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%b -> c
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%c -> inv
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&inv -> a
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"""
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EXAMPLE2 = """
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broadcaster -> a
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%a -> inv, con
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&inv -> b
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%b -> con
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&con -> output
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"""
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def visualize(modules):
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with open("g20.dot", 'w') as f:
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f.write("digraph G {\n")
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for m in modules.values():
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for cm in m[3]:
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f.write(" " + m[1] + ' -> ' + cm + "\n")
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f.write("}")
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def solve(input: Input, second=False):
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modules = {}
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for line in input.lines():
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if not line: continue
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src, dsts = line.split(" -> ")
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dsts = dsts.split(", ")
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if src.startswith("%"): # flip-flop
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modules[src[1:]] = [src[0], src[1:], 0, dsts]
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elif src.startswith("&"): # conjunction
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modules[src[1:]] = [src[0], src[1:], {}, dsts]
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elif src.startswith("broadcaster"):
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modules[src] = ["b", src, 0, dsts]
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else:
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raise Exception()
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for m in modules.values():
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for d in m[3]:
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if d in modules and modules[d][0] == "&":
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modules[d][2][m[1]] = 0
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if second:
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# visualize(modules)
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(feed,) = [m[1] for m in modules.values() if "rx" in m[3]]
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periods = {d: [] for d in modules[feed][2].keys()}
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BUTTON_PUSHES = 10000
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else:
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BUTTON_PUSHES = 1000
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lo, hi = 0, 0
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for i in range(BUTTON_PUSHES):
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qs = deque([("button module", "broadcaster", 0)])
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while qs:
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src, dst, sig = qs.popleft()
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if sig == 0:
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lo += 1
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else:
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hi += 1
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if not dst in modules:
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continue
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m = modules[dst]
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new_pulse = None
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if m[0] == "b":
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new_pulse = 0
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elif m[0] == "%":
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if sig == 0:
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m[2] = (m[2] + 1) % 2
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new_pulse = m[2]
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elif m[0] == "&":
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m[2][src] = sig
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if all(s == 1 for s in m[2].values()):
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new_pulse = 0
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else:
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new_pulse = 1
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else:
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raise Exception()
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if new_pulse is not None:
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for nxtdst in m[3]:
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if second and nxtdst == feed and new_pulse == 1:
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# print(f"{i:>4}: {dst[:4]:>4} -{new_pulse}> {nxtdst}")
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periods[dst].append(i)
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qs.append((dst, nxtdst, new_pulse))
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if second:
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# print(periods)
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# Yeah, we got a bit lucky that this works, I guess, but it does.
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return lcm(*[v[1] - v[0] for v in periods.values()])
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return lo * hi
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def main():
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DAY_INPUT = "i20.txt"
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print("Example 1:", solve(Input(EXAMPLE)))
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print("Example 2:", solve(Input(EXAMPLE2)))
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print("Solution 1:", solve(Input(DAY_INPUT)))
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print("Solution 2:", solve(Input(DAY_INPUT), True))
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assert solve(Input(DAY_INPUT), True) == 244178746156661
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if __name__ == "__main__":
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main()
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