Diagonal Sudoku also called Sudoku X.The puzzle is a 12x12 grid made up of 4x3 subgrids (called "regions").Some cells already contain numbers, known as "givens".The goal is to fill in the empty cells, one number in each, so that each column, row, region and diagonal contains the numbers 1 through 12 exactly once.Each number in the solution therefore occurs only once in each of three "directions", hence the "single numbers" implied by the puzzle's name.