[from nikoli website]
- Fill in all empty cells with numbers under the following rules:
- The area, connected by the same numbers horizontally or vertically, is called "Block". Separate the entire board by Blocks.
- Each Block contains as many cells as the number it contains (e.g., a Block of 6 has 6 cells).
- Blocks of the same size must not touch each other, horizontally or vertically.