Colour islands Sudoku

An extra constraint means this Sudoku requires you to think in diagonals as well as horizontal and vertical lines and boxes of nine.

Age
11 to 14
Challenge level
filled star empty star empty star
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem



By Henry Kwok

 

Colour Islands Sudoku



 

Rules of Colour Islands Sudoku



As in a standard Sudoku, the object of the puzzle is to fill in the whole 9x9 grid with numbers 1 through 9 so that each row, each column, and each of the nine 3x3 squares must contain all the nine different numbers 1 through 9.

There are two coloured "islands" in the 9x9 grid. Within each "island" there are two extra rules to apply:

 

  • no two diagonally adjacent cells can contain the same number
  • EVERY 3x3 square within the islands must contain the numbers 1 through 9.
For example the cell (5,3) contains the number 5 so the cell (6,4) in the yellow island cannot contain a 5 because it is diagonally adjacent to (6,4) - being to the right and down one.
The 9x9 grid with corners at C4R3, C4R5, C6R5 and C6R3 must contain all the digits 1 to 9.