A data structure is classified into two categories: Linear and Non-Linear data structures. A data structure is said to be linear if the elements form a sequence, for example Array, Linked list, queue etc. Elements in a nonlinear data structure do not form a sequence, for example Tree, Hash tree, Binary tree, etc. There are two ways of representing linear data structures in memory. One way is to have the linear relationship between the elements by means of sequential memory locations. Such linear structures are called arrays. The other way is to have the linear relationship between the elements represented by means of links. Such linear data structures are called linked list.