Ripple Effect

Rules

Place a number into each cell so that each bold region contains the numbers from 1 to n, where n is the number of cells in the region. Cells containing the same number x within the same row (or column) must have at least x cells between them in that row (or column). (For example, cells containing "1" cannot touch along an edge, cells containing "2" cannot touch or have exactly one cell between them in the same row or column, and so on.) Some numbers may be already filled in the grid.

(Rules and example from PGP IB)

History of the puzzle

First appeared on Nikoli volume 73 (1998). Rules suggested by ゲサク ("Gesaku"). Originally entitled 波及効果 ("Hakyuu Koka," namely "Ripple Effect").

Appearances in the past WPCs

• WPC 2019/Round 2 by Roland Voigt
• WPC 2019/Round 3 (Permaculture hybrid with Star Battle) by Silke Berendes
• WPC 2019/Round 7 by Ulrich Voigt
• WPC 2019/World Cup Playoffs by Erhard Notz
• WPC 2017/Round 12 by Amit Sowani
• WPC 2015/Round 9 ("Different Areas") by Vladimir Portugalov
• WPC 2013/Part 12