The objective of sudoku is to enter a digit from 1 through 9 in each cell, in such a way that:
In each sudoku puzzle, several digits have already been entered (the "givens"); these may not be changed.
The puzzler's job is to fill the remainder of the grid with digits –respecting, of course, the three constraints mentioned earlier.
- Each horizontal row (shown in pink) contains each digit exactly once
- Each vertical column (shown in yellow) contains each digit exactly once
- Each subgrid or region (shown in green) contains each digit exactly once