There is an obvious problem іn this task that can be seen in the condition itself:

The example K = 2, N = 3 (in the condition of the task) gives the result "01,02,21". But... Іn the test under the same conditions it is already expected line "01,12,02".

For the rest in the example K = 2, N = 5 it is expected "01,01,23,42,34". It's like of "01,20,12".

Three completely different options, all correct, but only one is suitable.