2019: d22: ex1: add solution

2019/d22/ex1/ex1.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python
+
+import dataclasses
+import enum
+import sys
+
+
+class Technique(enum.Enum):
+    DEAL_NEW = enum.auto()
+    CUT = enum.auto()
+    DEAL_INCR = enum.auto()
+
+
+@dataclasses.dataclass
+class Instruction:
+    tech: Technique
+    n: int
+
+    def to_linear(self) -> tuple[int, int]:
+        if self.tech == Technique.DEAL_NEW:
+            return (-1, -1)
+        if self.tech == Technique.CUT:
+            return (1, -self.n)
+        if self.tech == Technique.DEAL_INCR:
+            return (self.n, 0)
+        assert False  # Sanity check
+
+    def apply(self, card_pos: int, deck_size: int) -> int:
+        a, b = self.to_linear()
+        return (card_pos * a + b) % deck_size
+
+
+def solve(input: str) -> int:
+    def parse_instruction(input: str) -> Instruction:
+        if input == "deal into new stack":
+            return Instruction(Technique.DEAL_NEW, 0)
+        n = int(input.split()[-1])
+        if input.startswith("cut"):
+            return Instruction(Technique.CUT, n)
+        if input.startswith("deal with increment"):
+            return Instruction(Technique.DEAL_INCR, n)
+        assert False  # Sanity check
+
+    def parse(input: list[str]) -> list[Instruction]:
+        return [parse_instruction(line) for line in input]
+
+    def find_final_pos(
+        card_pos: int, deck_size: int, instructions: list[Instruction]
+    ) -> int:
+        for instr in instructions:
+            card_pos = instr.apply(card_pos, deck_size)
+        return card_pos
+
+    instructions = parse(input.splitlines())
+    return find_final_pos(2019, 10007, instructions)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()