From 786f88c00135b012524f301b41c99d3e46e1d399 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Wed, 21 Dec 2022 12:54:43 +0100
Subject: [PATCH] 2022: d21: ex2: add solution

---
 2022/d21/ex2/ex2.py | 167 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 167 insertions(+)
 create mode 100755 2022/d21/ex2/ex2.py

diff --git a/2022/d21/ex2/ex2.py b/2022/d21/ex2/ex2.py
new file mode 100755
index 0000000..386a187
--- /dev/null
+++ b/2022/d21/ex2/ex2.py
@@ -0,0 +1,167 @@
+#!/usr/bin/env python
+
+import dataclasses
+import enum
+import operator
+import sys
+from typing import Optional, Union
+
+Num = Union[int, "MathObserver"]
+
+
+class Operator(str, enum.Enum):
+    ADD = "+"
+    SUB = "-"
+    MUL = "*"
+    DIV = "/"
+
+    def __call__(self, lhs: Num, rhs: Num) -> Num:
+        OPERATIONS = {
+            self.ADD: operator.add,
+            self.SUB: operator.sub,
+            self.MUL: operator.mul,
+            self.DIV: operator.floordiv,
+        }
+        return OPERATIONS[self](lhs, rhs)
+
+    def reverse(self, lhs: Num, rhs: Num) -> Num:
+        OPERATIONS = {
+            self.ADD: Operator.SUB,
+            self.SUB: Operator.ADD,
+            self.MUL: Operator.DIV,
+            self.DIV: Operator.MUL,
+        }
+        return OPERATIONS[self](lhs, rhs)
+
+
+@dataclasses.dataclass
+class MathObserver:
+    _operations: list[tuple[Operator, int, bool]] = dataclasses.field(
+        default_factory=list
+    )
+    _target: Optional[int] = dataclasses.field(default=None, init=False)
+
+    def __add__(self, rhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.ADD, rhs, False)])
+
+    def __radd__(self, lhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.ADD, lhs, False)])
+
+    def __mul__(self, rhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.MUL, rhs, False)])
+
+    def __rmul__(self, lhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.MUL, lhs, False)])
+
+    def __sub__(self, rhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.SUB, rhs, False)])
+
+    def __rsub__(self, lhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.SUB, lhs, True)])
+
+    def __floordiv__(self, rhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.DIV, rhs, False)])
+
+    def __rfloordiv__(self, lhs: int) -> "MathObserver":
+        return MathObserver(self._operations + [(Operator.DIV, lhs, True)])
+
+    def __eq__(self, rhs: object) -> bool:
+        return self._record_eq(rhs)
+
+    def __req__(self, lhs: object) -> bool:
+        return self._record_eq(lhs)
+
+    def _record_eq(self, value: object) -> bool:
+        # Sanity checks
+        assert isinstance(value, int)
+        assert self._target is None
+        self._target = value
+        return True
+
+    def resolve(self) -> int:
+        assert self._target is not None  # Sanity check
+        target: int = self._target
+
+        for op, n, is_assymetric_rhs in reversed(self._operations):
+            if is_assymetric_rhs:
+                target = op(n, target)  # type: ignore
+            else:
+                target = op.reverse(target, n)  # type: ignore
+
+        return target
+
+
+class Monkey:
+    def get_value(self, monkeys: dict[str, "Monkey"]) -> Num:
+        raise NotImplementedError
+
+
+@dataclasses.dataclass
+class YellerMonkey(Monkey):
+    value: int
+
+    def get_value(self, monkeys: dict[str, "Monkey"]) -> int:
+        return self.value
+
+
+@dataclasses.dataclass
+class MathMonkey(Monkey):
+    lhs: str
+    op: Operator
+    rhs: str
+    _value: Optional[Num] = dataclasses.field(default=None, init=False)
+
+    def get_value(self, monkeys: dict[str, "Monkey"]) -> Num:
+        if self._value is None:
+            self._value = self.op(
+                monkeys[self.lhs].get_value(monkeys),
+                monkeys[self.rhs].get_value(monkeys),
+            )
+        return self._value
+
+
+class Human(Monkey):
+    def get_value(self, monkeys: dict[str, "Monkey"]) -> MathObserver:
+        return MathObserver()
+
+
+def solve(input: list[str]) -> int:
+    def parse_monkey(input: str) -> tuple[str, Monkey]:
+        name, value = input.split(": ")
+
+        monkey: Monkey
+        match value.split():
+            case [lhs, op, rhs]:
+                monkey = MathMonkey(lhs, Operator(op), rhs)
+            case [n]:
+                monkey = YellerMonkey(int(n))
+            case _:
+                assert False  # Sanity check
+
+        return name, monkey
+
+    monkeys = dict(map(parse_monkey, input))
+
+    monkeys["humn"] = Human()
+
+    root = monkeys["root"]
+    assert isinstance(root, MathMonkey)  # Sanity check
+
+    lhs, rhs = monkeys[root.lhs], monkeys[root.rhs]
+    assert lhs.get_value(monkeys) == rhs.get_value(monkeys)
+
+    for monkey in (lhs, rhs):
+        value = monkey.get_value(monkeys)
+        if not isinstance(value, MathObserver):
+            continue
+        return value.resolve()
+    assert False  # Sanity check
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()