Different Neighbours

Rules

Place a digit from 1-4 into each cell, exactly one digit per cell. Adjacent cells (including diagonally-adjacent cells) must not contain the same digit. Some digits are already given for you.

(Rule and example from PGP IB)

Rule Variations

• Numbers not Touching: From WPC 2018/Round 5. Normal Different Neighbours rules apply. Additionaly, 4 marked tetrominoes contain different numbers.

History of the Puzzle

Invented by Vladimir Portugalov (Belarus) in 2006. First appeared on WPC 2006/Part 1.

Appearances in the past WPCs

• WPC 2018/Round 5 by Jiří Hrdina
• WPC 2017/Round 3 by Deb Mohanty
• WPC 2017/Round 5 (Cairo Pentagonal) by Deb Mohanty
• WPC 2017/Round 10 ("Optimizer") by Deb Mohanty
• WPC 2015/Round 1
• WPC 2015/Round 11
• WPC 2015/Round 12
• WPC 2015/Round 14
• WPC 2013/Part 1