We are given a square board of size nxn, that is partially filled, 'across numbers' and 'down numbers' and we need to fill the board according to the following rules
- The board can have digits from 0-9 and -
- Only empty cells can be filled with other digits
- There are also some cells which are filled (blackened) and these are denoted with -, these cannot contain any digit and no other cell can be blackened
- We need to fill the board such that each of the 'across numbers' appears horizontally (left-right) (with digits in consecutive cells) on the filled board
- Also, each of the 'down numbers' must appear vertically (top-bottom) with digits in consecutive cells on the filled board