Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved More Linking Up with Linked Lists Chapter 11

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Chapter Contents 11.1 Some Variants of Singly-Linked Lists 11.2 Linked Implementation of Sparse Polynomials 11.3 Doubly-Linked Lists and the Standard C++ list 11.4 Case Study: Larger-Integer Arithmetic 11.5 Other Multiply-Linked Lists

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Chapter Objectives Survey common variants of linked lists and why they are used Study in detail an application of linked lists to implement sparse polynomials Describe doubly-linked lists and how they are used to implement C++ STL list container Build a class that makes it possible to do arithmetic with large integers Look briefly at some other applications of multiply- linked lists

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Lists with Head Nodes Consider linked lists from Chapter 6 –First node is different from others –Has no predecessor Thus insertions and deletions must consider two cases –First node or not first node –The algorithm is different for each

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Lists with Head Nodes Dual algorithms can be reduced to one –Create a "dummy" head node –Serves as predecessor holding actual first element Thus even an empty list has a head node

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Lists with Head Nodes For insertion at beginning of list –Head node is predecessor for new node newptr->next = predptr->next; predptr->next = newptr;

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Lists with Head Nodes For deleting first element from a list with a head node –Head node is the predecessor predptr->next = ptr->next; delete ptr;

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Circular Linked Lists Set the link in last node to point to first node –Each node now has both predecessor and successor –Insertions, deletions now easier Special consideration required for insertion to empty list, deletion from single item list

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Circular Linked Lists Traversal algorithm must be adjusted if (first != 0) // list not empty { ptr = first; do { // process ptr->data ptr = ptr->next; } while (ptr != first); } A do-while loop must be used instead of a while loop –Why is this required?

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Implementation of Sparse Polynomials Consider a polynomial of degree n –Can be represented by a list For a sparse polynomial this is not efficient

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Implementation of Sparse Polynomials We could represent a polynomial by a list of ordered pairs –{ (coef, exponent) … } Fixed capacity of array still problematic –Wasted space for sparse polynomial

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Implementation of Sparse Polynomials Linked list of these ordered pairs provides an appropriate solution –Each node has form shown Now whether sparse or well populated, the polynomial is represented efficiently

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Linked Implementation of Sparse Polynomials Note start of Polynomial class templatePolynomial class template –Type parameter CoefType –Term and Node are inner classes Addition operator –Adds coefficients of like degrees –Must traverse the two addend polynomials –Requires temporary pointers for each polynomial (the addends and the resulting sum)

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Addition Operator Requires temporary pointers for each polynomial (the addends and the resulting sum)

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Addition Operator As traversal takes place –Compare exponents –If different, node with smaller exponent and its coefficient attached to result polynomial –If exponents same, coefficients added, new corresponding node attached to result polynomial View source code View source code

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Doubly-Linked Lists Bidirectional lists –Nodes have data part, forward and backward link Facilitates both forward and backward traversal –Requires pointers to both first and last nodes

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Doubly-Linked Lists To insert a new node –Set forward and backward links to point to predecessor and successor –Then reset forward link of predecessor, backward link of successor

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Doubly-Linked Lists To delete a node –Reset forward link of predecessor, backward link of successor –Then delete removed node

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved The STL list Class Template A sequential container –Optimized for insertion and erasure at arbitrary points in the sequence. –Implemented as a circular doubly-linked list with head node.

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Comparing List With Other Containers Note : list does not support direct access –does not have the subscript operator [ ]. PropertyArray vector deque list Direct/random access ( [] )  (exclnt)  (good)X Sequential access  Insert/delete at front  (poor)  Insert/delete in middle  Insert/delete at end  Overheadlowestlowlow/mediumhigh

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved list Iterators list 's iterator is "weaker" than that for vector.  vector : random access iterators  list : bidirectional iterators Operations in common  ++Move iterator to next element (like ptr = ptr-> next )  --Move iterator to preceding element (like ptr = ptr-> prev )  *dereferencing operator (like ptr-> data )

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved list Iterators Operators in common  =assignment (for same type iterators) it1 = it2 makes i t1 positioned at same element as it2  == and != (for same type iterators) checks whether iterators are positioned at the same element  See basic list operations, Table 11-2, pg 621  View demonstration of list operations, Fig. 11-1Fig. 11-1

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Example: Internet Addresses Consider a program that stores IP addresses of users who make a connection with a certain computer –We store the connections in an AddressCounter object –Tracks unique IP addresses and how many times that IP connected View source code, Fig. 11.2Fig –Note uses of STL list and operators

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved The STL list Class Template Node structure struct list_node { pointer next, prev; T data; }

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved The STL list Class Template But it's allo/deallo-cation scheme is complex –Does not simply using new and delete operations. Using the heap manager is inefficient for large numbers of allo/deallo-cations –Thus it does it's own memory management.

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved The STL list Memory Management When a node is allocated 1.If there is a node on the free list, allocate it. This is maintained as a linked stack 2.If the free list is empty: a)Call the heap manager to allocate a block of memory (a "buffer", typically 4K) b)Carve it up into pieces of size required for a node of a list.

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved The STL list Memory Management When a node is deallocated –Push it onto the free list. When all lists of this type T have been destroyed –Return it to the heap

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Case Study: Large-Integer Arithmetic Recall that numeric representation of numbers in computer memory places limits on their size –32 bit integers, two's complement max We will design a BigInt class –Process integers of any size –For simplicity, nonnegative integers only

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved BigInt Design First step : select a storage structure –We choose a linked list –Each node sores a block of up to 3 consecutive digits –Doubly linked list for traversing in both directions

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved BigInt Design Input in blocks of 3 integers, separated by spaces –As each new block entered, node added at end Output is traversal, left to right

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved BigInt Design Addition adds the groupings right to left –Keeping track of carry digits

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved BigInt Implementation Standard list type provides all the tools we need Note class declaration, Fig. 11.3AFig. 11.3A View class definition, Fig. 11.3BFig. 11.3B Driver program to demonstrate use of the class, Fig 11.4Fig 11.4

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Multiply-Ordered Lists Ordered linked list –Nodes arranged so data items are in ascending/descending order Straightforward when based on one data field –However, sometimes necessary to maintain links with a different ordering Possible solution –Separate ordered linked lists – but wastes space

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Multiply-Ordered Lists Better approach –Single list –Multiple links

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Sparse Matrices Usual storage is 2D array or 2D vector If only a few nonzero entries –Can waste space Stored more efficiently with linked structure –Similar to sparse polynomials –Each row is a linked list –Store only nonzero entries for the row

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved For we represent with Sparse Matrices A =

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Sparse Matrices This still may waste space –Consider if many rows were all zeros Alternative implementation –Single linked list –Each node has row, column, entry, link Resulting list

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Sparse Matrices However … this loses direct access to rows Could replace array of pointers with –Linked list of row head nodes –Each contains pointer to non empty row list

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Sparse Matrices If columnwise processing is desired –Use orthogonal list –Each node stores row, column, value, pointer to row successor, pointer to column successor

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Sparse Matrices Note the resulting representation of the matrix A =

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Generalized Lists Examples so far have had atomic elements –The nodes are not themselves lists Consider a linked list of strings –The strings themselves can be linked lists of characters This is an example of a generalized list

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Generalized Lists Commonly represented as linked lists where –Nodes have a tag field along with data and link Tag used to indicate whether data field holds –Atom –Pointer to a list

Nyhoff, ADTs, Data Structures and Problem Solving with C++, Second Edition, © 2005 Pearson Education, Inc. All rights reserved Generalized Lists Lists can be shared –To represent (2, (4,6), (4,6)) For polynomials in two variables P(x,y) = 3 + 7x + 14y y 7 – 7x 2 y x 6 y 7