Every Star Battle solver eventually runs into a wall — a puzzle where the elimination technique alone isn't enough to make progress. When that happens, Region Confinement is often the key that unlocks the next chain of deductions. It's one of the most satisfying logical moves in the game: a quiet observation that cascades into a wave of eliminations across the board.

What Is Region Confinement?

Region Confinement is a technique based on a simple constraint from the rules: every region must contain exactly the right number of stars (one star in a 1-star puzzle, two stars in a 2-star puzzle, and so on). If you can determine that all of a region's stars are forced to sit inside a single row or column, then that row or column is effectively "used up" by that region — and you can eliminate every candidate cell in that row or column that belongs to a different region.

The logic flows in both directions, which is what makes this technique so powerful. A region can confine stars to a row, and a row can confine stars to a region. Understanding both directions doubles the number of situations where you can apply it.

Why It Works

In a standard 2-star puzzle, each row, each column, and each region must contain exactly two stars. If a region's available cells all happen to fall within a single row, then that region's two stars must both go into that row. The row already has its two stars accounted for by this one region — so no other region can contribute a star to that row. Every other cell in that row, regardless of which region it belongs to, can be safely eliminated as a star candidate.

The same reasoning applies to columns. And the reverse is equally valid: if a row's remaining candidate cells all happen to fall inside a single region, then that region must account for both of the row's stars, which means the region's remaining cells outside that row can all be eliminated.

How to Spot It

Scanning for Region Confinement requires you to look at each region and ask a focused question: are all of this region's possible star cells restricted to a single row or column? To do this efficiently:

  • Work region by region and note which rows or columns each region touches.
  • If a region's remaining open cells span only one row, you have region-to-row confinement.
  • If a region's remaining open cells span only one column, you have region-to-column confinement.
  • Then flip the scan: look at each row and ask whether its remaining candidates all fall inside a single region. Do the same for each column.

This dual scan is worth building into your solving routine. On harder puzzles you'll often find that neither direction yields anything early on, but after a few other eliminations shrink the candidate pools, confinement opportunities suddenly appear.

A Worked Example in Prose

Imagine a 7×7 2-star puzzle. In the top-left corner there is a small L-shaped region with five cells: three cells along the top row (columns 1, 2, and 3) and two cells directly below in row 2 (columns 1 and 2). You've already eliminated the two cells in row 2 because row 2 already has both of its stars elsewhere. That leaves only the three cells in row 1 as viable candidates for this region.

All three remaining candidates sit in row 1. The region is confined to row 1. Therefore, this region's two stars must both land in row 1 — and that means every other cell in row 1 (columns 4 through 7, belonging to other regions) can be eliminated immediately. You haven't placed a single star yet in this region, but you've dramatically narrowed the puzzle. In fact the two stars are already forced: the only non-touching pair among columns 1–3 is columns 1 and 3.

Now suppose that after those row-1 eliminations, you check the region that owns columns 4 and 5 of row 1. With those cells gone, maybe that region's only remaining candidates all fall in column 5. Column confinement now fires: column 5 is fully claimed by that region, so every other cell in column 5 across all other regions drops out. One confinement triggers another, and the puzzle opens up.

Region Confined to a Row vs. Region Confined to a Column

These two variants are logically identical — only the orientation differs. In practice, solvers tend to spot row confinement more readily because grids are naturally read left to right. Make a deliberate habit of rotating your perspective and scanning each region for column confinement too. Tall, narrow regions are obvious column confinement candidates; short, wide regions lean toward row confinement.

The Reverse: Row (or Column) Confined to a Region

The reverse direction is equally useful and slightly trickier to see. Here you look at a row and ask: do all of its remaining candidate cells belong to the same region? If yes, that region must place both of its stars somewhere in this row. That eliminates every other cell in the region that lies outside this row.

This variant often appears after a series of earlier eliminations have left a row with only a handful of open cells. When those cells all cluster inside one region, the cascade begins. It's worth checking every row and column at each step of a solve, not just at the start.

Mistakes to Avoid

  • Applying confinement before fully eliminating candidates. If you haven't applied all your known eliminations first, a region may appear confined when it isn't. Always keep your candidate markings up to date.
  • Confining on partial information. Double-check that you've accounted for every open cell in the region — not just the ones that are visible at a glance. A stray candidate in an adjacent row breaks the confinement entirely.
  • Forgetting the reverse direction. Many solvers apply region-to-row/column confinement but never think to run the row-to-region or column-to-region check. Both directions are equally powerful.
  • Eliminating the wrong cells. When a region is confined to row 3, you eliminate other regions' cells in row 3 — not the confined region's own cells elsewhere (those are already gone, which is why confinement fired).

When Does It Appear?

Region Confinement shows up across all difficulty levels, but it becomes a cornerstone technique on hard Star Battle puzzles. Easy puzzles often yield to basic elimination without needing confinement. As difficulty rises, regions become more intricately shaped and interleaved, which means simple row or column scans stall out — and that's exactly where confinement shines.

On expert-level grids, you'll frequently encounter chains of confinement: one region confined to a row triggers eliminations that confine a second region to a column, which triggers more eliminations that produce another confinement. Recognising and following these chains is a hallmark of advanced solving, and you can explore more strategies in our guide to advanced techniques.

Put It into Practice

The best way to internalise Region Confinement is to deliberately hunt for it on your next few puzzles, even when you think you can solve by other means. Pause after each elimination round and run a quick confinement scan — region by region, then row by row, then column by column. You'll be surprised how often it fires. Play a puzzle now and see how many confinement opportunities you can spot before reaching for any other technique.

Confinement is one of nine core moves — the illustrated Star Battle strategy guide shows where it sits in the full toolkit.