68 lines
2 KiB
Python
68 lines
2 KiB
Python
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#!/usr/bin/env python
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import sys
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from copy import deepcopy
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from typing import List
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def solve(input: List[int]) -> int:
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def highest_pow2(n: int) -> int:
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return len(bin(n)) - 2 - 1 # '0b' prefix, and off-by-one
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def count_bits_at(input: List[int], bit: int) -> int:
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return sum((n & pow(2, bit)) != 0 for n in input)
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def filter_by_bit_value(input: List[int], bit: int, value: int) -> List[int]:
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# Simplify the filter by mapping the value to the actual power of 2
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if value != 0:
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value = pow(2, bit)
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return list(filter(lambda n: (n & pow(2, bit)) == value, input))
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def filter_oxygen(input: List[int], bit: int) -> List[int]:
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# No further processing needed
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if len(input) <= 1:
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return input
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num_bits = count_bits_at(input, bit)
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# Keep 1s on equality
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if num_bits >= len(input) / 2:
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return filter_by_bit_value(input, bit, 1)
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else:
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return filter_by_bit_value(input, bit, 0)
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def filter_co2(input: List[int], bit: int) -> List[int]:
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# No further processing needed
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if len(input) <= 1:
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return input
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num_bits = count_bits_at(input, bit)
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# Keep 0s on equality
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if num_bits < len(input) / 2:
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return filter_by_bit_value(input, bit, 1)
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else:
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return filter_by_bit_value(input, bit, 0)
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oxygen, co2 = 0, 0
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max_bit = max(highest_pow2(n) for n in input)
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oxygen_input, co2_input = deepcopy(input), deepcopy(input)
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for bit in range(max_bit, -1, -1):
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oxygen_input = filter_oxygen(oxygen_input, bit)
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co2_input = filter_co2(co2_input, bit)
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if len(oxygen_input) == 1:
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oxygen = oxygen_input[0]
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if len(co2_input) == 1:
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co2 = co2_input[0]
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return oxygen * co2
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def main() -> None:
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input = [int(line, 2) for line in sys.stdin.readlines()]
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print(solve(input))
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if __name__ == "__main__":
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main()
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