Let's suppose I want to fill a n*n array with numbers occuring from 1 to n. One number is allowed to appear only once in every column/row. The solution becomes unique when there is only one possible way to complete the puzzle. I'm looking for the smallest number of clues(initially specified elements) to uniquely determine the solution in the function of n.
Example: For a 3x3 matrix this number is 2, since
1 0 0
0 2 0
0 0 0
by the set of instruction I provided above can be completed in only one way.