Multilist

代码说明：

If a multidimensional matrix is sparse, then we might use a multilist rather than a multidimensional array to represent it. We could use one node for each value in the matrix and one link for each dimension, with the link pointing to next item in that dimension. This arrangement reduces the storage required from the product of the maximum indices in the dimenstions to be proportional to the number of nonzero entries but increases the time required for many algorithms