solve() function

pigeon_magnet_solver/board.py

@@ -89,10 +89,13 @@ class Board:
         old_row = self.rows[row]
         self.rows[row] = old_row[:col] + value + old_row[col+1:]
 
-    def click(self, index: int) -> Self:
+    def click(self, index: int) -> Self | None:
         # check is clickable
         row, col = index // self.width, index % self.width
-        assert self.rows[row][col] == "1", f"{index} is not clickable!"
+
+        if self.rows[row][col] != "1":
+            # button is not clickable
+            return None
 
         # get neighbor positions
         nb_rc = [

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

tests/test_board.py

@@ -1,5 +1,3 @@
-import pytest
-
 from pigeon_magnet_solver.board import Board
 
 
@@ -13,9 +11,11 @@ def test_default():
     assert board.binary_repr == (4, 11, 3), "Wrong binary repr"
     assert board.solution_class == (1, 3, 2), "Wrong solution class"
 
-    assert board.click(4).binary_repr == (4, 14, 3)
-    assert board.click(5).binary_repr == (4, 11, 6)
+    assert (board2 := board.click(4)) is not None
+    assert board2.binary_repr == (4, 14, 3)
+
+    assert (board2 := board.click(5)) is not None
+    assert board2.binary_repr == (4, 11, 6)
 
     for idx in (3, 7):
-        with pytest.raises(AssertionError):
-            board.click(idx)
+        assert board.click(idx) is None