Interactive Problem 864: Combinatorics of Digits in a 4x4 Grid

a)

each digit appears 4 times, e.g.

1	1	1	1
2	2	3	3
4	2	2	3
4	4	4	3

b)

in addition, all digits appear in each row, e.g.

1	2	3	4
1	3	4	2
3	2	4	1
3	4	2	1

c)

moreover, no digit appears more than once in each column, e.g.

1	2	3	4
2	1	4	3
3	4	1	2
4	3	2	1

Fill in a grid where in addition to the constraints of a) - c) no identical digits are placed along the main diagonals.

Answer:

a)
b)
c)