Figure 6

Linked list (A) and skip list (B). The skip list contains nodes with a variable number of forward pointers. A node's level is the same as the number of forward pointers it has. Insertion and deletion into the linked list requires a simple traversal of the list, requiring O(n) time. Insertion and deletion into/from the skip list can make use of short-cuts provided by the structure. For example, to insert '30' into (B), one would start at the node having value '1', skip ahead to the node holding '9', skip ahead to '13' and then to '29' before encountering '41', which is greater than the value to insert. The traversal would then visit the node having '37' and finally insert between '29' and '37'. Such an operation can be shown to have O(n logn) expected time.