Overlap

Level: Basic

Push a block to each end and fill the cells that always overlap.

Overlap is the most powerful basic technique. When you push a block as far left as it can go and as far right as it can go, any cell that is filled in both cases must be filled no matter where the block sits.

If a block's length is more than half the line's length, its middle portion overlaps, so you can immediately confirm several cells. For example, in a line of length 5 with a clue of 4, the middle three cells (the 2nd through 4th) are filled in every case.

Even on a line with several blocks, you compare the two arrangements — all blocks packed to the left end versus packed to the right end — and find the cells that overlap. This is the key technique for opening up large puzzles.

Related techniques

Basic

Reading the Clue Sum

First work out the minimum length that a line's number clues require.

Intermediate

Extending from the Edge

An X near the edge pushes back where the first block can start.