road trip: F2L revisited

Just back from a family road trip. I found myself in the passenger seat for the first and last 8-hour legs — the car seat behind it makes the legroom too small for my wife to sit there comfortably. Boredom. Good thing I brought a cube and Andy Klise’s awesome cheat sheet summarizing Badmephisto’s F2L algorithms.

Learn F2L intuitively. Those seem to be the F2L watchwords. And so I did. Intuitively. The basic idea of setting up pairs in the top layer and then inserting them into a slot made sense. And the basic approaches for hiding a corner while moving an edge eventually became second nature. But not efficient. With half the edge/corner pairs (on average) in the front/left faces, I had to do the exceptionally awkward (F’ U’ F) trigger to get them into the front-right slot or do a y turn to get the pair into the left/back faces for a (L’ U L) trigger. Either way, I’d have to slow down, switch hands, re-position, etc. No surprise, my fastest solves are the ones with all or most of the insertions resulting from pairs in the right/front faces with the super easy (R U R’) trigger.

As I watched more and more youtube videos, I realized that the faster solvers do their F2L insertions with mostly U and R face turns. Makes sense…especially for right-handed folks. “Screw intuitive,” I said, “time for some cheat sheets.” Enter the Klise/Badmephisto F2L Guide.

I learned a handful of great new tricks from the cheat sheet, which I’ll explain in a couple examples below. I still haven’t so much memorized the algorithms. Instead, I’ve tried to understand the three or four basic setups and approaches thereto. Everything else is just variation on theme. The guide simply revealed more efficient (but still intuitive) approaches.

EXAMPLE 1: use early Dw to setup easier insertion trigger

Take this pretty basic setup:

We know that the edge needs to be moved one space counter-clockwise closer to the edge to set up the pairing and insertion. Normally, I’d solve this with U’ (R U’ R’) U (F’ U’ F), which would hide the corner in the back right (U’ R), move the edge once counter-clockwise (U’), unhide the edge (R’), and return the edge back above the insertion slot with a (U). That would set up the pair for a simple but awkward (F’ U F):

In contrast, Badmephisto’s approach makes this a mostly right/top face affair, with Dw (R’ U’ R U’) (R’ U’ R). By starting with the Dw R’ (instead of U’ R), the algorithm puts the empty slot for hiding the edge in the right front. As with my old approach, the U’ brings the edge into the right relative position to the corner, which is restored with an R. With the insertion slot now on the back right (because of the Dw), a U’ sets up a far easier (R’ U’ R) insertion trigger:

Same number of moves, but without the front face turns that slow me down.

EXAMPLE 2: Use front/right slot for hiding corner, eliminating awkward front face turns

Here’s another pretty basic setup:

We know that the edge and pair need to be separated by two spaces. Normally, I’d solve this with U (F’ U2 F) U’ (R U R’), which would hide the corner in the front-left (U F’), move the edge two spaces (U2), unhide the edge (F), and return the edge back above the insertion slot with a (U’). That would set up the pair for a simple (R U R’) insertion:

The first example overcame an awkward insertion trigger by inserting into the back-right slot, instead of the usual front-right. In this example, the insertion is easy and lighting fast, but the F turns to hide the corner are not. Badmephisto’s Dw (R’ U2 R) Dw’ (R U R’) approach is clever, with an early Dw to open the front-right slot for hiding the corner. The basic concept remains unchanged: Hide the corner, move the edge twice, and then unhide the corner. But the Dw allows simple R’ and R turns for hiding and unhiding the corner. Here’s the situation just after the corner is unhidden:

From there, a Dw’ AUFs to the same simple (R U R’) insertion as my old approach. Again, the same number of moves, but without the slow front face turns.


2 thoughts on “road trip: F2L revisited

  1. Pingback: 28 seconds « adventures in cubing

  2. Pingback: One Year In: Nuthin’ But a ‘G’ Thang « adventures in cubing

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