Creek

Creek is a binary shading puzzle where numbers are placed at the intersections of the grid lines (where four cells meet). Each number indicates how many of the four surrounding cells should be shaded. The player must determine which cells to shade and which to leave white, with the additional constraint that all white (unshaded) cells must form a single connected group through horizontal and vertical adjacency.

Rules

1. The grid is rectangular, and numbers are placed at some or all intersections of the grid lines.
2. Each intersection is surrounded by up to four cells (fewer at edges and corners).
3. A number at an intersection tells exactly how many of its surrounding cells must be shaded.
4. Cells without any numbered intersection constraint can be either shaded or unshaded.
5. All unshaded (white) cells must form a single connected group — you must be able to reach any white cell from any other white cell by traveling through horizontally or vertically adjacent white cells.

Strategies

• Zero Clue: If an intersection shows 0, all surrounding cells must be white.
• Maximum Clue: If an intersection shows 4 (or 3 at an edge, or 2 at a corner), all surrounding cells must be shaded.
• One Remaining: If a clue's count is almost met (e.g., a "3" with two cells already shaded), the remaining cells' status can be deduced.
• Connectivity Check: Before shading a cell, ensure it would not disconnect the white cells. If shading a cell would cut the white region into two separate parts, that cell must remain white.
• Bottleneck Cells: White cells that form narrow bridges between larger white areas cannot be shaded, as doing so would break connectivity.
• Combined Clue Analysis: Adjacent intersections share cells between them. Cross-reference their clues to narrow down which shared cells are shaded.

Creek is a logic puzzle that emerged from the Japanese puzzle community, following the tradition of binary shading puzzles (shade or don't shade) that also includes Nurikabe, Hitori, and similar formats. The puzzle is sometimes attributed to Nikoli or to independent puzzle designers working in the competitive puzzle circuit.

The name "Creek" evokes a stream or waterway, which is a fitting metaphor: the connected white cells can be visualized as a flowing creek winding through shaded terrain. This poetic naming convention is common in Japanese puzzle design, where puzzle names often suggest a visual metaphor for the solving experience.

Creek has appeared in the World Puzzle Championship and in Puzzle GP events organized by the World Puzzle Federation. It is valued in competition settings because it tests both local arithmetic reasoning (counting shaded neighbors around each clue) and global spatial reasoning (maintaining connectivity of the white region).

The puzzle occupies an interesting middle ground among shading puzzles: it is simpler in concept than Nurikabe (which has island size constraints) but adds the intersection-based clue system that gives it a distinct flavor. Creek puzzles can range from gentle introductory sizes (5x5) to challenging large grids where connectivity analysis becomes the dominant solving technique.