solve() function

pigeon_magnet_solver/main.py

@@ -1,18 +1,23 @@
 #!/usr/bin/python3
 
 from .board import Board
+from .solver import solve
 
 
 def main() -> None:
-    board = Board.default_puzzle
-    print(board)
-    print(board.solution_class, board.binary_repr)
+    solution = solve(
+        Board.default_puzzle,
+        lambda state: state.solution_class == (3, 1, 2),
+    )
 
-    for btn in (2, 4, 5, 7):  # 2 is not a regular button, but alas
+    if solution is None:
+        print("Unsolvable!")
+        return
+
+    for btn, state in solution:
         print(f"clicking button {btn} ...")
-        board.click(btn)
-        print(board)
-        print(board.solution_class, board.binary_repr)
+        print(state)
+        print(state.solution_class, state.binary_repr)
 
 
 if __name__ == "__main__":

pigeon_magnet_solver/solver.py

@@ -0,0 +1,39 @@
+from typing import Callable
+
+from .board import Board
+
+
+def solve(
+    state: Board,
+    is_solved: Callable[[Board], bool],
+    *,
+    history: list[tuple[int, Board]] | None = None,
+) -> list[tuple[int, Board]] | None:
+
+    if history is None:
+        # create starting state
+        history = [(-1, state)]
+
+    if is_solved(state):
+        return history
+
+    for button in state.buttons:
+        # try to click all buttons
+        next = state.click(button)
+
+        if next is not None:
+            # click successful
+            binary_history = (
+                state.binary_repr
+                for _, state in history
+            )
+
+            if next.binary_repr not in binary_history:
+                # "next" is a new state
+                solution = solve(
+                    next, is_solved,
+                    history=[*history, (button, next)]
+                )
+
+                if solution is not None:
+                    return solution