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#!/usr/bin/python3
def main() -> None:
with open("input", "r") as f:
prog = [
int(x) for x in (
next(l for l in f.readlines() if l.startswith("Program"))
.split(':' )[1]
.split(',')
)
][::-1]
print(search(prog))
def step(a: int) -> int:
b = (a & 7) ^ 2
return (a>>b ^ b ^ 7) & 7
def search(prog: list[int], a: int = 0) -> int | None:
if len(prog) == 0:
return a
for i in range(0b111 + 1):
n = a<<3 | i
if (
step(n) == prog[0]
and (b := search(prog[1:], n)) is not None
):
return b
if __name__ == "__main__":
main()
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