[mcphage]

It creates puzzles with multiple possible solutions:

5 6 3 _

4 _ _ _

6 7 4 _

_ 4 _ _

The bottom right corner can be in the loop, or out of the loop, and both solutions are valid.

[MohammadAbuG]

yes, the solutions are not unique, it would be very hard to make sure the puzzle has a unique solution probably requiring a brute force algorithm, the puzzle itself is NP complete, the way I generate the puzzle is to first create the "loop" with all cells having numbers in them then removing numbers from cells at random.