Consider a puzzle, puzzle, where you start with a n x n matrix with a random allocation of three characters, x0 s, y 0 s, and z 0 s, in the grid locations. the goal of the puzzle is to remove the characters, one at a time, so that each row contains only characters of one letter, such as only x0 s, and each column contains at least one character. show that puzzle ∈ np.