Star Battle

The no-touch rule does the work

Star Battle sits on a grid split into bold regions, and the goal is to place stars so every row, every column, and every region holds the same number: one on the easy boards, two or more on the harder ones, with the status line telling you how many. The rule that ties it all together is that no two stars may touch, not even diagonally, so every star sits alone in a pocket of empty cells. That constraint is also your main tool. Place one star and you have instantly ruled out all eight cells around it. Click a cell once to drop a dot as a reminder that it stays empty, click again to place a star, and a third click clears it. The fastest progress comes from marking what cannot be a star rather than hunting for what can, so use the dots freely and constantly.

Three named tricks

Serious solvers lean on a small set of patterns, and they all show up here. The first is the 2x2 rule: because stars cannot touch, any 2x2 box of cells holds at most one star. A region shaped like a small square therefore pins its star options hard, and on two-star boards, a region that fits inside a 2x3 strip is instantly tight, since two stars need real elbow room. The second is region-versus-line counting. If a region lives entirely inside one row, that row's quota of stars must come from that region, so every cell of the row outside the region is a dot. Stretch the same idea further: if two regions together fit inside two rows, those two rows' stars all come from those two regions, and every other region is pushed out of both rows. The third is the plain count. A row that still needs one star with only one undotted cell left has its star found, and the same arithmetic runs down columns and inside regions. Because all three kinds of area demand the same total, satisfying one often forces the others in a chain.

A worked opening

Here is how a typical one-star board cracks open. Scan for the smallest region. Say it is a two-cell domino lying in a single row. Whatever happens, that row's star sits in the domino, so dot every other cell of the row immediately. Now check the two domino cells themselves: both touch the cells above and below, so whichever one becomes the star will clear a three-cell block in the neighbouring rows. Suppose a second small region pokes only one cell into the row above. If the domino's left cell would wipe out that region's last available cell, the left cell is impossible, and the star goes right. No guessing happened, just three rules stacked on each other. That stacking is the whole game, and it is why the hard boards feel like proofs rather than searches. It also helps to know the total. On a one-star board of, say, ten rows, exactly ten stars exist, one per region too, so once nine regions are settled the last one is bookkeeping. Counting placed stars against that fixed total is a quick health check when a board starts to feel wrong.

• Ring every placed star with dots on all eight neighbours before doing anything else.
• Start from the smallest regions; they have the fewest ways to hold their stars.
• Watch for regions trapped in one row or column. They claim that line's stars and dot out everyone else.
• On two-star boards, remember each region needs room for two non-touching stars. Cramped regions give up their secrets first.

A championship favorite

Star Battle is a young puzzle by pencil-game standards. It was created by the Dutch puzzle designer Hans Eendebak and first appeared around the 2003 World Puzzle Championship, and it has been a competition staple ever since, a favourite at events run by the World Puzzle Federation. The reason setters love it is the reason it looks so clean: there are no number clues at all. The regions and the no-touch rule carry the entire puzzle, and the two-star boards demand layered reasoning across rows, columns, and regions at once. Inkplay's version is timed, so tidy habits beat flashes of insight: dot relentlessly, count what each line still needs, and the board falls one forced cell at a time.