Counting the Bag: Knowing What Is Coming

The randomiser guarantees each shape once per seven, which makes the unseen pieces deducible rather than merely probable.

Because the seven-bag deals each shape exactly once per bag, the pieces you have not seen yet are not a mystery. They are a shrinking list.

The basic deduction

If the current bag has produced six pieces and none was the I, the seventh is the I. Certainly, not probably.

More usefully: if four pieces of the bag have appeared and the I was not among them, it is one of the remaining three. You know it is coming within three pieces, which is a completely different planning problem to "it might come".

What to count

Tracking all seven shapes is more effort than it is worth in real time. The useful reduced version is to track one thing: has the I appeared in this bag?

That single bit of information drives the most important decision in the game, which is whether to keep deepening your well or clear now.

Using it

I not yet seen this bag. Safe to keep the well open and keep stacking. It is coming within a few pieces.

I already used this bag. The next one could be up to eleven pieces away. Stop deepening. Get the height down.

That is the whole technique, and it converts the well strategy from a gamble into a calculation.

Where the bag boundary is

You can track it by counting pieces in sevens from the start, but under pressure it is easier to watch for a shape repeating. When you see a second I, a new bag has begun.

The five-piece preview helps enormously here: you can often see the bag boundary before you reach it.

In versus

Counting matters more in a duel, because both players receive the same sequence. If you know an I is coming and your opponent is stacking flat, you know they are about to have a four-row clear available. That shapes whether you attack now or hold garbage in reserve.

The limit

Do not over-invest in this. Counting one shape reliably beats attempting to count all seven and losing track. The point is a better answer to one specific question, not perfect information.

Read next

• Keep the Stack Flat: The One Habit That Matters MostA flat surface accepts every piece. A jagged one accepts a few. Most runs end because the board stopped accepting what the bag offered.
• Never Bury a HoleA covered gap costs you every row above it. Taking a worse placement to avoid one is nearly always correct.
• Downstacking: How to Dig Yourself OutClearing your way down to a buried hole is a distinct skill, and it is the one that turns bad runs into recovered ones.
• The Nine-Column Stack and the Open WellFill nine columns flat, leave one open, and wait for the long piece. The standard shape for a high score.
• The Seven Pieces, One by OneWhat each shape is good for, what it ruins, and why S and Z are the ones that end runs.
• Two Players, One KeyboardSplit-screen has a texture online play cannot reproduce, and a couple of practical quirks.