Star Battle

Star Battle is a logic puzzle where the player must place stars in a grid divided into irregularly shaped regions. Each row, each column, and each region must contain the same number of stars (typically one or two). Stars cannot touch each other, not even diagonally. The puzzle requires no arithmetic — only spatial reasoning and careful elimination. Its clean rules and visual elegance have made it a favorite in puzzle competitions.

Rules

1. The grid is divided into N regions of varying shapes (typically an NxN grid with N regions).
2. Place stars in the grid so that each row contains exactly the target number of stars (1-star or 2-star variants).
3. Each column must also contain exactly the target number of stars.
4. Each region must also contain exactly the target number of stars.
5. No two stars may be adjacent — not horizontally, vertically, or diagonally. Each star must have no other star in any of its 8 surrounding cells.

Variants

• 1-Star: Each row, column, and region contains exactly 1 star. Typically on smaller grids (6x6 to 8x8).
• 2-Star: Each row, column, and region contains exactly 2 stars. The standard competition format, usually on 10x10 grids.

Strategies

• Small Regions: A region with very few cells has limited star placement options. In a 2-star puzzle, a region with only 2 or 3 cells is heavily constrained.
• Non-Adjacency Elimination: Once a star is placed, all 8 surrounding cells are eliminated. This cascading elimination is the primary solving mechanism.
• Row/Column Counting: If a row already has its star quota, all remaining cells in that row are eliminated.
• Region-Row/Column Intersection: If a region only overlaps with one row in a limited way, stars in that region's row-section are constrained.
• Complementary Regions: If two small regions together span exactly the cells needed for their combined star count in certain rows or columns, the positions become determinable.
• Process of Elimination: Often the key technique — systematically check where stars *cannot* go, and the valid positions emerge.

Star Battle was created by Hans Eendebak, a Dutch puzzle designer, around 2003. The puzzle quickly gained traction in the competitive puzzle-solving community, appearing in national and international puzzle championships.

The puzzle became a staple of the World Puzzle Championship (WPC), where it is one of the most popular and frequently featured puzzle types. Its appeal in competitions lies in its scalability — 1-star puzzles on small grids serve as warm-ups, while 2-star puzzles on large grids with complex region shapes can challenge even the world's best solvers.

Star Battle gained significant mainstream visibility through the New York Times, which began featuring a variant called "Two Not Touch" (a 1-star version) in its puzzle section. This introduction to a mass audience brought the puzzle to millions of new solvers who had never encountered competitive puzzle formats.

The puzzle's popularity continues to grow in both competitive and casual contexts. Its rule set — no arithmetic, no language, pure spatial logic — makes it universally accessible across languages and cultures. Puzzle designers appreciate the creative freedom in shaping regions, which allows for an enormous variety of puzzle constructions at every difficulty level. Today, Star Battle is considered one of the essential puzzle types in the modern logic puzzle canon.