2 Outline Abstract Data Type (ADT) List ADT List ADT with Array ImplementationLinked listsBasic operations of linked listsInsert, find, delete, print, etc.Variations of linked listsCircular linked listsDoubly linked lists
3 The List ADT A sequence of zero or more elements A1, A2, A3, … AN N: length of the listA1: first elementAN: last elementAi: position iIf N=0, then empty listLinearly orderedAi precedes Ai+1Ai follows Ai-1
4 Operations printList: print the list makeEmpty: create an empty list find: locate the position of an object in a listlist: 34,12, 52, 16, 12find(52) 3insert: insert an object to a listinsert(x,3) 34, 12, 52, x, 16, 12remove: delete an element from the listremove(52) 34, 12, x, 16, 12findKth: retrieve the element at a certain position
5 Implementation of an ADT Choose a data structure to represent the ADTE.g. arrays, records, etc.Each operation associated with the ADT is implemented by one or more subroutinesTwo standard implementations for the list ADTArray-basedLinked list
6 Array ImplementationElements are stored in contiguous array positions
7 Array Implementation...Requires an estimate of the maximum size of the listwaste spaceprintList and find: O(n)findKth: O(1)insert and delete: O(n)e.g. insert at position 0 (making a new element)requires first pushing the entire array down one spot to make roome.g. delete at position 0requires shifting all the elements in the list up oneOn average, half of the lists needs to be moved for either operation
8 Example Implementation List_3358Array-based implementationUses an iterator to move cursorHas a fixed size
9 Pointer Implementation (Linked List) Ensure that the list is not stored contiguouslyuse a linked lista series of structures that are not necessarily adjacent in memoryEach node contains the element and a pointer to a structure containing its successorthe last cell’s next link points to NULLCompared to the array implementation,the pointer implementation uses only as much space as is needed for the elements currently on the listbut requires space for the pointers in each cell
10 Linked Lists A linked list is a series of connected nodes BCHeadA linked list is a series of connected nodesEach node contains at leastA piece of data (any type)Pointer to the next node in the listHead: pointer to the first nodeThe last node points to NULLnodeAdatapointer
11 Linked Implementation... Requires no estimate of the maximum size of the listNo wasted spaceprintList and find: O(n)findKth: O(n)insert and delete: O(1)e.g. insert at position 0 (making a new element)Insert does not require moving the other elementse.g. delete at position 0requires no shifting of elementsInsertion and deletion becomes easier, but finding the Kth element moves from O(1) to O(n)
12 Next Assignments List_3358 Linked implementation with simulated pointersWill use two arrays and cursorLinked implementation with actual pointers
13 Variations of Linked Lists Circular linked listsThe last node points to the first node of the listHow do we know when we have finished traversing the list? (Tip: check if the pointer of the current node is equal to the head.)ABCHead
14 Variations of Linked Lists Doubly linked listsEach node points to not only successor but the predecessorThere are two NULL: at the first and last nodes in the listAdvantage: given a node, it is easy to visit its predecessor. Convenient to traverse lists backwardsABCHead
15 Array versus Linked Lists Linked lists are more complex to code and manage than arrays, but they have some distinct advantages.Dynamic: a linked list can easily grow and shrink in size.We don’t need to know how many nodes will be in the list. They are created in memory as needed.In contrast, the size of a C++ array is fixed at compilation time.Easy and fast insertions and deletionsTo insert or delete an element in an array, we need to copy to temporary variables to make room for new elements or close the gap caused by deleted elements.With a linked list, no need to move other nodes. Only need to reset some pointers.
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