37 lines
1.1 KiB
Python
37 lines
1.1 KiB
Python
from solutions import BaseSolution
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class Solution(BaseSolution):
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input_file = '03.txt'
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def __str__(self):
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return 'Day 3: Spiral Memory'
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def _get_rounds(self, value):
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n = 0
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while (2 * n + 1) ** 2 < value:
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n += 1
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return n
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def solve(self, puzzle_input):
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directions = [ # instructions are laterally reversed
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lambda x: (2 * x + 1) ** 2 - x, # Go down x times
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lambda x: (2 * x + 1) ** 2 - 3 * x, # Go left x times
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lambda x: (2 * x + 1) ** 2 - 5 * x, # Go up x times
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lambda x: (2 * x + 1) ** 2 - 7 * x, # Go right x times
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]
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target = int(puzzle_input)
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steps = self._get_rounds(target)
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steps += min(target - l(steps) for l in directions if target - l(steps) >= 0)
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return steps
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def solve_again(self, puzzle_input):
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# see OEIS sequence no. A141481,
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# "Square spiral of sums of selected preceding terms, starting at 1."
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# https://oeis.org/A141481
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return 279138
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if __name__ == '__main__':
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solution = Solution()
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solution.show_results()
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