112 lines
3.3 KiB
Python
112 lines
3.3 KiB
Python
"Day 3: Gear Ratios"
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from __future__ import annotations
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from dataclasses import dataclass
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from typing import NamedTuple
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class SchematicNumber(NamedTuple):
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number: str
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row: int
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col: int
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def extend_digit(self, digit: str) -> SchematicNumber:
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return SchematicNumber(self.number + digit, self.row, self.col)
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class SchematicSymbol(NamedTuple):
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symbol: str
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row: int
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col: int
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@dataclass
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class Schematic:
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numbers: list[SchematicNumber]
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symbols: list[SchematicSymbol]
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@classmethod
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def parse(cls, input: str) -> Schematic:
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row = 0
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col = 0
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current_number: SchematicNumber | None = None
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numbers: list[SchematicNumber] = []
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symbols: list[SchematicSymbol] = []
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for char in input:
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match char:
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# Digit
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case n if n in "0123456789":
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if not current_number:
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current_number = SchematicNumber("", row, col)
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current_number = current_number.extend_digit(char)
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col += 1
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# Blank
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case ".":
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if current_number:
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numbers.append(current_number)
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current_number = None
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col += 1
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# Newline
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case "\n":
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if current_number:
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numbers.append(current_number)
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current_number = None
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row += 1
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col = 0
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# Schematic smybol
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case _:
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if current_number:
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numbers.append(current_number)
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current_number = None
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symbols.append(SchematicSymbol(char, row, col))
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col += 1
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# Finalize a number at the end of the schematic
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if current_number:
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numbers.append(current_number)
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return cls(numbers, symbols)
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def part_numbers(self) -> list[tuple[SchematicNumber, SchematicSymbol]]:
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results = []
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for number in self.numbers:
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for symbol in self.symbols:
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if (
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# Symbol within 1 row
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(number.row - 1 <= symbol.row <= number.row + 1)
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and
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# Symbol within 1 column
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(number.col - 1 <= symbol.col <= number.col + len(number.number))
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):
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results.append((number, symbol))
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break
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return results
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def solve_part_1(input: str) -> int:
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schematic = Schematic.parse(input)
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return sum(int(part_number.number) for part_number, _ in schematic.part_numbers())
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def solve_part_2(input: str) -> int:
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schematic = Schematic.parse(input)
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part_groups: dict[SchematicSymbol, list[SchematicNumber]] = {}
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for part_number, part_symbol in schematic.part_numbers():
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if part_symbol.symbol != "*":
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continue
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if part_symbol not in part_groups:
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part_groups[part_symbol] = []
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part_groups[part_symbol].append(part_number)
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gears = [
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part_numbers for part_numbers in part_groups.values() if len(part_numbers) == 2
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]
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return sum(int(gear_1.number) * int(gear_2.number) for gear_1, gear_2 in gears)
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