Puzzle 1: Take a 4x4 grid of 0’s and replace ten of them with 1’s so that the sum of each row, column, and major diagonal* is an odd number.
Puzzle 2: The same as puzzle 1 with the rows, columns, and major diagonals each summing to an even number.
Bonus: Select your answers for puzzles 1 and 2 in such a way that the answer for Puzzle 1 can be changed to an answer for Puzzle 2 by moving the positions of just two of the 1’s.
* by “Major Diagonal” I mean one that starts in one corner of the grid and ends in the opposite corner. There are two major diagonals.
* = Solved just one of the puzzles.
Puzzle 1 has 96 answers (counting rotations) here is one of them.
Puzzle 2 has 64 answers (again counting rotations).