Place a digit in each empty cell such that every thickly outlined region of size N contains all digits from 1 to N. The same digits do not touch each other, even diagonally.
(Rules and example from WPC 2017 IB)
- Suguru Diagonal: From WPC 2018/Round 2. Marked diagonal contains each of the numbers from 1 to the size of the grid.
- Capsules: A different name for the puzzle; it sometimes refers to a specific variant of Suguru where all regions have a size of 5 cells.
History of the puzzle
Invented by Naoki Inaba (Japan) in 2001 under the name "ナンバーブロック" ("Number Block").  The name "Suguru", a contraction of "Suji gurupu" ("Number group") is given by Puzzler Magazine (UK) since, according to them, the original name "did not sufficiently reflect the qualities of" the puzzle. 
Appearances in the past WPCs
- WPC 2018/Round 2 (Suguru, Suguru Diagonal) by Jiří Hrdina
- WPC 2017/Round 9 by Swaroop Guggilam
- WPC 2016/Round 12
- WPC 2013/Final