PERFECT CLEARS · LESSON 1 OF 2
Perfect Clear basics and parity
AFTER THIS GUIDEYou can distinguish a necessary counting condition from a reachable Perfect Clear solution.
Account for every cell.
A Perfect Clear leaves no locked blocks anywhere on the board after line clearing. A Tetris clears four rows; it is a PC only if nothing survives above or elsewhere. Look at the whole result, not just the attack label.
Each tetromino supplies four cells. On a ten-column board, a plan starting with B occupied cells and placing n pieces must satisfy B + 4n = 10L if it ends empty after clearing L rows. With no garbage added, an empty-board four-row PC uses ten pieces. This is an area check, not a solution.
An isolated region must also be tileable. If a fixed wall encloses a pocket of six empty cells and no clearing or opening of the wall occurs before you fill it, whole four-cell pieces cannot fill just that pocket. The condition changes if a clear opens the region, so be explicit about what stays fixed.
Checkerboard parity gives another filter. Colour the board like a chessboard. Most tetrominoes cover two cells of each colour; a T covers three of one and one of the other. Count the imbalance needed by a candidate tiling. But line clears shift surviving rows and can change their colour alignment, so a single static colouring cannot be applied blindly across a multi-clear sequence.
Reject, then verify
Check the area
For an empty four-row rectangle, count forty cells: ten pieces. If your plan has only nine pieces and no existing blocks, it is short by four cells before you even consider shapes.
Compare the checkerboard footprints
The O diagram covers two cells of each colour; the T covers a three-to-one split. Use that difference to test a fixed remaining region. Passing the count does not prove the pieces fit.
Check the actual finish
Step through the Perfect Clear example. Identify every surviving cell before the last clear and confirm that none remains afterwards. Finally verify that each piece can reach its proposed landing in the available order.
Dots retain the underlying checkerboard colors. Counting them can rule out some tilings; equal totals alone do not guarantee a solution.
One O-shaped space remains.
Both remaining rows are full.
Zero blocks left. Perfect Clear.
Common mistakes
Calling a four-line clear a PC automatically
Blocks above the four rows can survive. Inspect the complete board after clearing.
Using parity as a magic solver
It rules some plans out. It does not establish geometry, rotation entry or queue order for the remaining plans.
Forgetting intermediate clears
A row disappearing changes the board. Recount the remaining region after each clear instead of keeping an obsolete outline.
TAKE IT TO THE BOARD
Count before searching
- Open Perfect Clear mode with Gravity Off and NEXT 5. Play manually.
- At three promising low positions, count the existing blocks and propose how many further pieces and cleared rows an empty finish would require.
- Reject plans that fail the count. For those that pass, inspect shape and entry order before following a suggestion.
- If the PC disappears, choose a clean ordinary clear and explain which constraint failed.
What counts as progress? You reject an impossible plan for a specific reason and do not mistake a valid count for a guaranteed solution.
Open practice ↗Opens the mode. Set Gravity and NEXT yourself; your current settings are kept.
Keep these terms nearby
NEXT IN THIS PATH
Perfect Clear loops
Understand bag boundaries and repeatable continuations.
Read the next guide →Further reading
This example and drill were created for Stacking Lab, using the trainer’s implemented behaviour.