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https://github.com/thib8956/advent-of-code.git
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121 lines
3.2 KiB
Python
121 lines
3.2 KiB
Python
from dataclasses import dataclass
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from typing import Literal
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@dataclass()
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class Item:
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kind: Literal["file", "free"]
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size: int
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id_: int = 0
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def parse_disk(data):
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disk = {}
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disk2 = []
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id_cnt = 0
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offset = 0
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for pos, size in enumerate(data):
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if pos % 2 == 0: # file
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id = id_cnt
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for i in range(int(size)):
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disk[offset + i] = id
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disk2.append(Item("file", int(size), id))
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id_cnt += 1
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offset += int(size)
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else: # free space
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if int(size) > 0:
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disk2.append(Item("free", int(size)))
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offset += int(size)
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return disk, disk2
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def part1(disk):
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max_file_location = max(disk.keys())
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write_ptr = 0
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read_ptr = max_file_location
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while True:
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while write_ptr in disk:
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write_ptr += 1
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while read_ptr not in disk:
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read_ptr -= 1
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if write_ptr >= read_ptr:
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break
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disk[write_ptr] = disk[read_ptr]
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del disk[read_ptr]
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checksum = sum(i * disk.get(i, 0) for i in range(max_file_location))
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return checksum
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def part2(disk):
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max_id = max(f.id_ for f in disk)
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for i in range(max_id, -1, -1):
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file, file_index = next((file, index) for index, file in enumerate(disk) if file.id_ == i)
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# find index of the first gap large enough
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free_index, free_space = next(((i, b) for i, b in enumerate(disk) if b.kind == "free" and b.size >= file.size), (None, None))
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if free_index is None:
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continue
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if free_index >= file_index: # always move file to the left
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continue
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# decrease free space by file size (in case free space is larger)
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disk[free_index].size -= file.size
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# add a free space in place of the file
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disk[file_index] = Item("free", file.size)
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# insert file just before free space
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disk.insert(free_index, file)
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#debug = debug_print(disk)
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#print(debug)
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# calculate checksum for part2
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total_checksum = 0
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offset = 0
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#print(disk)
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debug_print(disk)
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#print(len(disk))
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for f in disk:
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if f.kind != "file":
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offset += f.size
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continue
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# S(n) = n*(n+1) // 2
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#print(f"checksum = {f.id_} * ({offset} * {f.size} + ({f.size} * ({f.size - 1})) // 2")
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checksum = f.id_ * (offset * f.size + (f.size * (f.size - 1)) // 2)
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#print(f, checksum, total_checksum)
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offset += f.size
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total_checksum += checksum
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return total_checksum
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def main(inp):
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disk, disk2 = parse_disk(inp)
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print("Part 1: ", part1(disk))
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print("Part 2: ", part2(disk2))
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def debug_print(disk):
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res = []
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for item in disk:
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if item.kind == "free" and item.size > 0:
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res.extend(["."] * item.size)
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else:
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res.extend([str(item.id_)] * item.size)
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return "".join(res)
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if __name__ == "__main__":
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import sys
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infile = sys.argv[1] if len(sys.argv) > 1 else None
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content = "2333133121414131402"
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if infile is not None:
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with open(infile) as f:
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content = f.read().rstrip()
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main(content)
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