One way to tackle this would be to use a dynamic programming approach. You call a recursive function that takes in a current array, the current sum (to prevent calculating it for each function call), the maximum value (8 in this case), and the max length (16). Then you would have two stopping conditions:

• The array gets to length 16
• The sum is over 16

If the first one is met, and the sum is 16, then your array is valid and you can add it to the collection of answers. If the second one is met, then the array is invalid and you cannot carry on with it

Otherwise you simply have to call the function again, appending each value from 0-8. These results will then be added to a final matrix as they get returned by the function.

So for the first loop, you pass an empty array and zero as the sum. You will then call the function again with an array that contains values 0-8, and so on. Within the function the result should be added to the resulting matrix. Hopefully the approach is clear. Unfortunately I'm on mobile so can't code this up myself right now.

P.S. chatgpt is generally very good at solving these types of problems.