- nb_errors += abs(len(stack) - len(target_stack))
- nb_errors += sum([0 if x == y else 1 for x, y in zip(stack, target_stack)])
+ e = abs(len(result_stack) - len(target_stack)) + sum(
+ [0 if x == y else 1 for x, y in zip(result_stack, target_stack)]
+ )
+ nb_errors += e
+ stacks.append((start_stack, target_stack, result_stack, e == 0))