Reordering pieces with hold
Hold lets you place pieces in a different order from the one they arrive in: how to think about reordering for perfect clears, with typical patterns.
Pieces arrive in a fixed order, but hold lets you change the order you place them in. In perfect-clear stacking you will often find that the pieces you need are visible but come in the wrong order. This page sorts out which orders hold can produce and which it cannot. For the basic rules of hold, read “How to use Hold” first.
What hold can do: put one piece off until later
Hold sets the current piece aside, and only one piece at a time. You can bring the stored piece back whenever you like. In other words, hold is a way to put one piece off for as long as you like.
With these three pieces, you can produce the following four placing orders.
| Placing order | How |
|---|---|
| I → T → S | Do not use hold. |
| I → S → T | Place the I. Hold the T and place the S. Bring out the T and place it. |
| T → I → S | Hold the I and place the T. Bring out the I and place it (the S goes into hold). Bring out the S and place it. |
| T → S → I | Hold the I, then place the T and the S in turn. Finally, bring out the I and place it. |
Orders that start with S (S → I → T and S → T → I), on the other hand, cannot be produced. To get to the S you would have to put off both the I and the T, and hold takes only one piece.
Example 1: a piece that cannot get in unless another goes first
This leftover is filled by a T and an I, but only in one order. Suppose they arrive as I → T. If you try to place the I first, it has no way into the lower row, because only two cells of that row are open from above.
Perfect-clear stacking is full of ordering constraints like this one: “placing this piece clears a row, which opens the way in for the next piece”. If the pieces arrive the other way round, swap them with hold.
So what if they arrive as I → S → T? The T is third. Hold the I and the next piece is the S, but the S fits nowhere in this leftover. You would like to hold the S as well, but hold is already taken by the I. With this order, a perfect clear is impossible.
Example 2: parking a piece you will not use in hold
Suppose the pieces arrive as T → O → L. The T is no use for this leftover. In a case like this, put the T in hold and leave it there to the end. Hold the T, place the O, place the L, and you have a perfect clear.
A four-line PC is completed with ten pieces, but thanks to hold you actually get to pick ten out of eleven. Being able to decide “I will not use this one” for a single piece raises the success rate a great deal. But you can only park one piece. If two unusable pieces arrive in a row, you have no choice but to place one of them.
Example 3: storing a piece you will need later
Hold can only put pieces off, so it cannot bring a far-away piece forward. What you can do instead is store a piece when it arrives if you expect to need it.
For example, if you know the leftover needs an I, hold the I as soon as it arrives. After that, shape the leftover with the other pieces, and bring the I out of hold the moment its spot is ready. Pieces like the I and the T, which fit in few places but decide the outcome, are well suited to this.
How to build a plan
- Decide which pieces to use. Think of a combination that fills the remaining cells. You can leave out at most one piece.
- Check the constraints on the placing order. Pieces that end up underneath, and pieces that clear a row to open an entrance, have to be placed first.
- Check that the arriving order can produce it. Apply “the first piece you place is one of the first two” one move at a time.
If hold already contains a piece, think of it as one extra piece at the front of the queue, and you can check in the same way.