(Dictionaries.py) A sparse array is an array where most elements are zero. We can often reduce memory requirements by storing the positions and values of all non-zero elements of a sparse array. Write the function sparse array(A) that receives a 2D array of integers A and returns a dictionary D containing the non-zero elements of A and their indices such that if A[i,j] = k and k > 0, D[(i,j)] = k.