97 lines
2.5 KiB
Python
97 lines
2.5 KiB
Python
#!/usr/bin/env python
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# https://adventofcode.com/2025/day/4
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f = open("day04input.txt", "r")
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#f = open("testinput.txt", "r")
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d = [l.strip() for l in f.readlines()]
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def day04(data: list[str], remove_rolls: bool = False) -> int:
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row_no = len(data)
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col_no = len(data[0])
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data_list = list("".join(data))
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assert row_no * col_no == len(data_list)
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offsets = {-col_no - 1, -col_no, -col_no + 1, -1, 1, col_no - 1, col_no, col_no + 1}
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offset_l = {-col_no - 1, -1, col_no - 1}
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offset_r = {-col_no + 1, 1, col_no + 1}
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offset_t = {-col_no - 1, -col_no, -col_no + 1}
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offset_b = {col_no - 1, col_no, col_no + 1}
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# little debug function that prints the current floor plan
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def field_to_str(data_list: list) -> str:
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field = ""
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for j in range(col_no):
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field += "".join(data_list[j*col_no:(j+1)*col_no-1]) + "\n"
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return field
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# print(f"initial state")
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# print(field_to_str(data_list))
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def count_rolls(data_list: list) -> int:
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iteration_rolls = 0
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# loop over data
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for i in range(len(data_list)):
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# skip if there's no roll on this position
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if data_list[i] == ".":
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continue
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local_offsets = offsets.copy()
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# check left edge
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if i % col_no == 0:
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local_offsets -= offset_l
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# check right edge
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if i % col_no == col_no - 1:
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local_offsets -= offset_r
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# check top edge
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if i - col_no < 0:
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local_offsets -= offset_t
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# check bottom edge
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if i + col_no >= len(data_list):
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local_offsets -= offset_b
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assert len(local_offsets) in (3, 5, 8)
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# loop over adjacent positions
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adjacent_rolls = 0
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for o in local_offsets:
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# adjacent position is empty
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if (c := data_list[i + o]) == ".":
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continue
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# adjacent position is a roll
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elif c in "x@":
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adjacent_rolls += 1
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# adjacent position is unknown character
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else:
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raise Exception("arrgh!")
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# mark roll as removable
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if adjacent_rolls < 4:
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iteration_rolls += 1
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data_list[i] = "x"
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return iteration_rolls
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# solve part 1
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if not remove_rolls:
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return count_rolls(data_list)
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# solve part 2
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total_rolls = 0
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while True:
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iteration_rolls = count_rolls(data_list)
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if iteration_rolls > 0:
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# increase number of removed rolls
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total_rolls += iteration_rolls
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# remove marked rolls
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data_list = list(map(lambda c: "." if c == "x" else c, data_list))
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else:
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return total_rolls
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print(day04(d))
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print(day04(d, True))
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