Understanding and Solving the Rubik's Cube Without Algorithms
5. Go, Swap and Back
In this chapter, we will delve into the "Go, Swap and Back" movement, which allows us to change specific parts of a layer without affecting the rest of that layer. By understanding this technique, together with the knowledge we have gained so far, we will be able to solve a significant portion of the Rubik's Cube, approximately 80% or 21 out of the 26 parts.
To explain the idea of the "go, swap and back" movement, let's consider an example. Suppose we want to place the orange corner (Figure 5.1) exactly where the green corner is on the U layer without disrupting the rest of that layer.
Merely applying the R2 move is not sufficient to achieve our goal. Although the orange corner would be in the desired position, most of the U layer would be disrupted since it is perpendicular to the R layer. Try this approach by clicking play (▷) in Figure 5.1.
Now, let's apply the F move and observe the outcome. Click forward (⧐) in Figure 5.2. By applying F, we place the green corner on the D layer and one side of the U layer on the E layer. This is the "Go" movement.
With this configuration in place, we can rotate the D layer to swap the desired corners. Since the D layer is parallel to the U and E layers, this movement will not affect them. By applying D', we place the orange corner in the desired position without disrupting the U and E layers. Click forward again (⧐) in Figure 5.2. This completes the "Swap" movement.
To maintain the integrity of the U layer and achieve our goal of placing the orange corner, we apply the back and forth principle. In this case, we make the opposite movement to the initial one. By applying F', the U layer returns to its original condition, and the orange corner ends up in its desired position. Click forward (⧐) twice in Figure 5.2.
Recapping the moves: F' ("Go") D' ("Swap") F ("Back"). To see the complete sequence with short pauses, click reset (∣◁) in Figure 5.2, and then click play (▷).
While other parts of the cube may have been affected, our initial goal of preserving the U layer and placing the desired corner has been achieved.
Notice that, to bring the orange corner to the desired place, we first need to move that place to the layer where the orange corner is located. This is when the place "goes." Only after that, we can perform the swap by rotating a layer parallel to the one we want to preserve. The original layer (U) can be restored simply by moving the perpendicular layer (F) "back" to its original position.
It's important to note that for the back and forth movement, we use a layer that is perpendicular to the one we want to preserve. Additionally, the orange cubelet cannot be on the back and forth layer. In this case, we have chosen the F layer to perform the back and forth movement.
To summarize the key points of the "go, swap, and back" strategy:
The back and forth movement involves a layer perpendicular to the one we want to preserve.
The cubelet we want to place cannot be on the back and forth layer.
The target position "goes" to the layer containing the desired cubelet.
The "swap" with the desired cubelet is performed using a movement parallel to the layer we want to preserve.
After the swap, the target position goes "back" to its original position by reversing the rotation of the same layer chosen for the back and forth movement.
App source: animcubejs.cubing.net/animcubejs.html