aoc(2024-07): 🎄

2024-py/advent/index.py

@@ -5,6 +5,7 @@
 from advent.solutions.day04 import Day04
 from advent.solutions.day05 import Day05
 from advent.solutions.day06 import Day06
+from advent.solutions.day07 import Day07
 
 index: dict[str, type[Solution]] = {
     ### START SOLUTIONS ###
@@ -14,5 +15,6 @@
     "04": Day04,
     "05": Day05,
     "06": Day06,
+    "07": Day07,
     ### END SOLUTIONS ###
 }

2024-py/advent/solutions/day07.py

@@ -0,0 +1,84 @@
+from dataclasses import dataclass
+from enum import Enum
+from itertools import product
+
+from aocd import get_puzzle
+
+from advent.solution import Solution
+
+
+class Operation(Enum):
+    ADD = (0,)
+    MULT = (1,)
+    CONCAT = (2,)
+
+
+@dataclass
+class Equation:
+    calibration: int
+    operands: list[int]
+
+    def evaluate(self, operations: list[Operation] | tuple[Operation, ...]):
+        value = self.operands[0]
+        for i in range(1, len(self.operands)):
+            match operations[i - 1]:
+                case Operation.ADD:
+                    value += self.operands[i]
+                case Operation.MULT:
+                    value *= self.operands[i]
+                case Operation.CONCAT:
+                    value = int(f"{value}{self.operands[i]}")
+
+            if value > self.calibration:
+                return False
+
+            # Idea: greedy-add remaining operands to see if the sum is too large?
+        return value == self.calibration
+
+
+class Day07(Solution):
+    def parse(self, puzzle_input: str):
+        equations: list[Equation] = []
+        for line in puzzle_input.splitlines():
+            calibration, operands = line.split(": ")
+            equations.append(Equation(int(calibration), list(map(int, operands.split()))))
+
+        return equations
+
+    def run(self, puzzle_input: str):
+        equations = self.parse(puzzle_input)
+
+        # Idea: lazy evaluate and bail once equation becomes too large
+        # Idea: dynamic programming to memoize when operand combinations have already been tried?
+
+        return (
+            sum(eq.calibration for eq in self.part_one(equations)),
+            sum(eq.calibration for eq in self.part_two(equations)),
+        )
+
+    def part_two(self, equations: list[Equation]):
+        possible: list[Equation] = []
+        for equation in equations:
+            for operations in product(Operation, repeat=len(equation.operands) - 1):
+                if equation.evaluate(operations):
+                    possible.append(equation)
+                    break
+
+        return possible
+
+    def part_one(
+        self,
+        equations: list[Equation],
+    ):
+        possible: list[Equation] = []
+        for equation in equations:
+            for operations in product((Operation.ADD, Operation.MULT), repeat=len(equation.operands) - 1):
+                if equation.evaluate(operations):
+                    possible.append(equation)
+                    break
+
+        return possible
+
+
+if __name__ == "__main__":
+    print(Day07().run(get_puzzle(day=7, year=2024).examples[0].input_data))