My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Update day18.py
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2016/day18.py
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2016/day18.py
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import fileinput
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def is_safe(row, i):
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def is_trap(row, i):
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"""Helper function to read out-of-bounds tiles as safe."""
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if 0 <= i < len(row):
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return row[i]
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return True
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return False
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def predict_next_row(row):
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"""Given a row, returns the predicted following row."""
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return [not (is_safe(row, i-1) ^ is_safe(row, i+1)) for i in range(len(row))]
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return [is_trap(row, i-1) ^ is_trap(row, i+1) for i in range(len(row))]
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if __name__ == '__main__':
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# Represent safe tiles as True and traps as False
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raw_first_row = fileinput.input()[0].strip()
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row = tuple(True if c == '.' else False for c in raw_first_row)
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safe_tiles = sum(row)
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# Represent traps as True and safe tiles as False.
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# The number of safe tiles per row is len(row) - sum(row).
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row = [True if c == '^' else False for c in fileinput.input()[0].strip()]
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row_len = len(row)
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safe_tiles = row_len - sum(row)
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for _ in range(40 - 1):
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row = predict_next_row(row)
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safe_tiles += sum(row)
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safe_tiles += row_len - sum(row)
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print "Number of safe tiles in first 40 rows:", safe_tiles
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for _ in range(400000 - 40):
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row = predict_next_row(row)
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safe_tiles += sum(row)
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safe_tiles += row_len - sum(row)
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print "Number of safe tiles in all 400000 rows:", safe_tiles