1 / 72

CH2. ARRAYS

CH2. ARRAYS . 2.1 Abstract Data Types and the C++ Class. 2.1.1 C++ Class : represents an ADT Consists of four components class name data members member functions levels of program access public : anywhere private : within its (friend) class a function

cwen
Télécharger la présentation

CH2. ARRAYS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CH2. ARRAYS

  2. 2.1 Abstract Data Types and the C++ Class 2.1.1 C++ Class : represents an ADT • Consists of four components • class name • data members • member functions • levels of program access • public : anywhere • private : within its (friend) class a function • protected : within its class friend

  3. 2.1 Abstract Data Types and the C++ Class(Cont’) #ifndef RECTANGLE_H #define RECTANGLE_H    // In the header file Rectangle.h class Rectangle {        public:             // the following members are public // The next four members are member functions         Rectangle();       // constructor         ~Rectangle();      // destructor         int GetHeight();  // returns the height of the rectangle         int GetWidth();   // returns the width of the rectangle private:    // the following members are private // the following members are data members         int x1, y1, h, w;         // (x1, y1) are the coordinates of the bottom left corner of the rectangle         // w is the width of the rectangle; h is the height of the rectangle }; #endif Program 2.1 : Definition of the C++ class Rectangle

  4. 2.1 Abstract Data Types and the C++ Class(Cont’) 2.1.2 Data Abstraction and Encapsulation in C++ • Data encapsulation of C++ class • all data members are private (or protected) • external access to data members are by member functions • Separation of specification and implementation of member functions • specification (function prototype) • name of functions • type of function arguments • type of function result • Implementation • placed in a source file of the same name • can be included inside its class definition

  5. 2.1 Abstract Data Types and the C++ Class(Cont’) // In the source file Rectangle.C #include "Rectangle.h" // The prefix “Rectangle::" identifies GetHeight() and // GetWidth() as member functions // belonging to class Rectangle. It is required because the member functions // are implemented outside their class definition int Rectangle::GetHeight() {return h;} int Rectangle::GetWidth() {return w;} Program 2.2 : Implementation of operations on Rectangle

  6. 2.1 Abstract Data Types and the C++ Class(Cont’) 2.1.3 Declaring class objects • in the same way as variables • Invoking member functions • using component selection operators • dot(.) : direct selection • arrow : indirect selection through a pointer

  7. 2.1 Abstract Data Types and the C++ Class(Cont’) // In a source file main.C #include <iostream.h> #include "Rectangle.h" main() {         Rectangle r, s;   // r and s are objects of class Rectangle         Rectangle *t = &s;   // t is a pointer to class object s         ….. // use . to access members of class objects. // use → to access members of class objects through pointers.         if (r.GetHeight()*r.GetWidth() >t→GetHeight() * t→GetWidth())          cout << " r ";         else cout << " s ";         cout << "has the greater area" << endl; } Program 2.3 : A C++ code fragment demonstrating how Rectangle objects are declared and member functions invoked

  8. 2.1 Abstract Data Types and the C++ Class(Cont’) 2.1.4 Special Class Operations • Constructor • a member function which initializes data members of an object • If provided for a class, automatically executed when an object of that class is created • must be public • the name must be identical to the name of the class • must not specify a return type or return a value Rectangle::Rectangle(int x, int y, int height, int width) {         x1=x; y1=y;         h=height; w=width; } Program 2.4 : Definition of a constructor for Rectangle

  9. 2.1 Abstract Data Types and the C++ Class(Cont’) • initialize Rectangle object using constructor • Rectangle r(1, 3, 6, 6); • Rectangle *s = new Rectangle(0, 0, 3, 4); • initialize using a default constructor • Rectangle r; Rectangle::Rectangle (int x=0, int y=0,                          int height=0, int width=0) : x1 (x), y1(y), h(height), w(width) { } Program 2.5 : A default constructor

  10. 2.1 Abstract Data Types and the C++ Class(Cont’) • Destructor • a member function which deletes data members • automatically invoked when a class object goes out of scope or is deleted • must be public • its class name prefixed with ~ • if a data member is a pointer, only the space of the pointer is returned • Operator overloading • polymorphism : same operator for different situations • for example, algorithm comparing two floats is different from algorithm comparing two ints

  11. 2.1 Abstract Data Types and the C++ Class(Cont’) int Rectangle::operator==(const Rectangle &s ) {         if (this == &s) return 1;         if ((x1 == s.x1) && (y1 == s.y1) && (h == s.h) && (w == s.w)) return 1;         else return 0; } Program 2.6 : Overloading operator == for class Rectangle

  12. 2.1 Abstract Data Types and the C++ Class(Cont’) • this • represents a pointer to the object that invoked a member function • *this represents the object

  13. 2.1 Abstract Data Types and the C++ Class(Cont’) Ostream& operator<<(ostream& os, Rectangle& r) { os << “Position is : ” << r.xl << “ ”; os << r.yl << endl; os << “Height is : ” << r.h << endl; os << “Width is : ” << r.w << endl; return os; } Program 2.7 : Overloading operator << for class Rectangle

  14. 2.1 Abstract Data Types and the C++ Class(Cont’) 2.1.5 Miscellaneous Topics • static class data member • a global variable for its class • there is only one copy of a static data member and all class objects share it • declaration does not constitute a definition

  15. 2.1 Abstract Data Types and the C++ Class(Cont’) 2.1.6 ADTs and C++ classes • They are similar • Some operators in C++, when overloaded for user defined ADTs, are declared outside the C++ class definition of the ADT

  16. 2.1 Abstract Data Types and the C++ Class(Cont’) class NaturalNumber{ // An ordered subrange of the integers starting at zero and ending at // the maximum integer (MAXINT) on the computer public:         NaturalNumber Zero();    // returns 0         Boolean IsZero(); // if *this is 0, return TRUE; otherwise, return FALSE         NaturalNumber Add(NaturalNumber y); // return the smaller of *this+y and MAXINT;         Boolean Equal(NaturalNumber y); // return TRUE if *this==y; otherwise return FALSE         NaturalNumber Successor(); // if *this is MAXINT return MAXINT; otherwise return *this+1         NaturalNumber Substract(NaturalNumber y);   // if *this<y, return 0; otherwise return *this-y }; ADT 1.2 : Abstract data type NaturalNumber

  17. 2.2 Array As Abstract Data Type • Array • a set of pairs <index, value> • ADT for array provides operations • retrieves a value • stores a value • C++ Array • index starts at 0 • C++ does not check bounds for an array index • example • float example[n]; • ith element: example[i] and *(example+i)

  18. 2.2 Array As Abstract Data Type(Cont’) Class GeneralArray { // objects: A set of pairs <index, value> where for each value of index // in IndexSet there is a value of type float. // IndexSet is a finite ordered set of one or more dimensions, // for example, {0, ..., n-1} for one dimension, // {(0,0), (0,1), (0,2), (1,0), (1,1), (1,2), (2,0), (2,1), (2,2)} for two // dimensions, etc. public:       GeneralArray(int j, RangeList list, float initValue = defaultValue);       // The constructor GeneralArray creates a j dimensional array       // of floats; the range of the kth dimension is given by the       // kth element of list. For each index i in the index set, insert       // <i, initValue> into the array.

  19. 2.2 Array As Abstract Data Type(Cont’) float Retrieve(index i);       // if (i is in the index set of the array) return the float       // associated with i in the array; else signal an error.       void Store(index i, float x);       // if (i  is in the index set of the array) delete any pair of the       // form <i, y> present in the array and insert the new pair         // <i, x>; else signal an error. }; // end of GeneralArray ADT 2.1 : Abstract data type GeneralArray

  20. 2.3 Polynomial Abstract Data Type • Ordered (or linear) list • days of the week : (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday) • years Switzerland fought in WWII : () • Operations on lists (a0, a1, ..., an-1) : • find the length, n, of the list • read the list from left to right (or reverse) • retrieve the ith element, 0≤i<n • store a new value into the ith position, 0≤i<n • insert a new element at the position i, 0≤i<n • delete the element at position i, 0≤i<n

  21. 2.3 Polynomial Abstract Data Type(Cont’) • Polynomial • requires ordered lists • the largest exponent is called degree • sum and product of polynomials A(x) = ∑aixi  and  B(x) = ∑bixi • A(x) + B(x) = ∑(ai + bi)xi • A(x) ‧ B(x) = ∑(aixi ․∑(bjxj))

  22. 2.3 Polynomial Abstract Data Type(Cont’) Class Polynomial {      // objects : p(x) = a0xe0 + … + anxe0 ; a set of ordered pairs of <ei, ai>, // where ai ∈ Coefficient and ei∈Exponent      // We assume that Exponent consists of integers ≥ 0    public:       Polynomial();   // return the polynomial p(x)=0 int operator!(); // If *this is the zero polynomial, return 1; else return 0;       Coefficient Coef(Exponent e);       // return the coefficient of e in *this       Exponent LeadExp();       // return the largest exponent in *this

  23. 2.3 Polynomial Abstract Data Type(Cont’) Polynomial Add(Polynomial poly); // return the sum of the polynomials *this and poly       Polynomial Mult(Polynomial poly);   // return the product of the polynomials *this and poly       float Eval(float f);   // Evaluate the polynomial *this at f and return the result.   }; // end of polynomial ADT 2.2 : Abstract data type Polynomial

  24. 2.3 Polynomial Abstract Data Type(Cont’) 2.3.1 Polynomial Representation • Principle • unique exponents are arranged in decreasing order

  25. 2.3 Polynomial Abstract Data Type(Cont’) • Representation 1 (Array: static memory allocation) • define the private data members of Polynomial private : int degree ; // degree≤MaxDegree float coef[MaxDegree+1] ; • for Polynomial object a, n≤MaxDegree a.degree=n a.coef[i]=an-i, 0≤i≤n • a.coef[i] is the coefficient of xn-I A(x)=anxn+an-1xn-i+...+a1x+a0 • leads to a very simple algorithms for many of the operations on polynomials • wastes computer memory • for example, if a.degree MaxDegree

  26. 2.3 Polynomial Abstract Data Type(Cont’) • Representation 2 (Array: dynamic memory allocation) • define coef with size a.degree+1 • declare private data members private : int degree ; float *coef ; • add a constructor to Polynomial Polynomial::Polynomial(int d) { degree=d ; coef=newfloat[degree+1] ; } • wastes space for sparse polynomials • for example, x1000+1

  27. 2.3 Polynomial Abstract Data Type(Cont’) • Representation 3 • previously, exponents are represented by array indices • now, (non-zero) exponents are stored • all Polynomials will be represented in a single array called termArray • termArray is shared by all Polynomial objects • it is declared as static • each element in termArray is of type term class term { friend Polynomial ; private : float coef ; // coefficient int exp ; // exponent };

  28. 2.3 Polynomial Abstract Data Type(Cont’) • declare private data members of Polynomial • class Polynomial { private : static term termArray[MaxTerms]; static int free; int Start, Finish; public: Polynomial ADD(Polynomial poly); ... } • required definitions of the static class members outside the class definition term Polynomial::termArray[MaxTerms]; int Polynomial::free=0; // next free location in termArray • A(x)=2x1000+1, B(x)=x4+10x3+3x2+1

  29. 2.3 Polynomial Abstract Data Type(Cont’) A.Start A.Finish B.Start B.Finish Free coef 2 1 1 10 3 1 exp 1000 0 4 3 2 0 0 1 2 3 4 5 6 Figure 2.1 : Array representation of two polynomials

  30. 2.3 Polynomial Abstract Data Type(Cont’) • A(x) has n nonzero terms • A.Finish=A.Start+n-1 • if n=0, A.Finish=A.Start-1 • comparison with Representation 2 • Representation 3 is superior when many zero terms are present as in A(x) • when all terms are nonzero, as in B(x), Representation 3 uses about twice as much space as Representation 2

  31. 2.3 Polynomial Abstract Data Type(Cont’) 2.3.2 Polynomial Addition • Representation 3 is used • C(x)=A(x)+B(x)

  32. 2.3 Polynomial Abstract Data Type(Cont’) Polynomial Polynomial::Add(Polynomial B) // return the sum of A(x) (in *this) and B(x) { Polynomial C; int a = Start; int b = B.Start; C.Start = free; float c; while ((a<=Finish) && (b<=B.Finish) switch (compare(termArray[a].exp, termArray[b].exp)){ case '=': c = termArray[a].coef + termArray[b].coef; if (c) NewTerm(c, termArray[a].exp); a++; b++; break; case '<': NewTerm(termArray[b].coef, termArray[b].exp); b++; break;

  33. 2.3 Polynomial Abstract Data Type(Cont’) case '>': NewTerm(termArray[a].coef, termArray[a].exp); a++; }// end of switch and while // add in remaining terms of A(x) for (; a<=Finish; a++) NewTerm(termArray[a].coef, termArray[a].exp); // add in remaining terms of B(x) for (; b<=B.Finish; b++) Newterm(termArray[b].coef, termArray[b].exp); C.Finish = free - 1; return C; }// end of Add Program 2.8 : Adding two polynomials

  34. 2.3 Polynomial Abstract Data Type(Cont’) void Polynomial::NewTerm(float c, int e) // Add a new term to C(x). { if (free>=MaxTerms) { cerr << "Too many terms in polynomials" << endl; exit(1); } termArray[free].coef = c; termArray[free].exp = e; free++; }// end of NewTerm Program 2.9 : Adding a new term

  35. 2.3 Polynomial Abstract Data Type(Cont’) • Analysis of Add • m and n are number of nonzero-terms in A and B, respectively • the while loop of line 5 is bounded by m+n-1 • the for loops of lines 21 and 24 are bounded by O(n+m) • summing up, the asymptotic computing time is O(n+m) • Disadvantages of representing polynomials by arrays • space must be reused for unused polynomials • linked lists in chapter 4 provide a solution

  36. 2.4 Sparse Matrices 2.4.1 Introduction • Matrix with m rows and n columns • m×n (m by n) • mn elements • when m=n, the matrix is square • Storing a matrix • two dimensional array A[m][n] • an element is A[i][j] • sparse matrix • store only the nonzero elements

  37. 1 1 2 3 4 5 0 1 2 0 15 0 0 12 0 -15 0 -27 3 4 1 0 11 3 0 0 0 1 6 82 -2 2 0 0 0 -6 0 0 2 109 -64 11 3 0 0 0 0 0 0 3 12 8 9 4 91 0 0 0 0 0 4 48 27 47 5 0 0 28 0 0 0 2.4 Sparse Matrices(Cont’) • Matrix operations • Creation • Transposition • Addition • multiplication (a) (b) Figure 2.2 : Two matrices

  38. 2.4 Sparse Matrices(Cont’) Class SparseMatrix { // objects : A set of triples, <row, column, value>, where row // and column are integers and form a unique combination; value // is also an integer. public: SparseMatrix(int MaxRow, int MaxCol); // the constructor function creates a SparseMatrix // that can hold up to MaxItems=MaxRow x MaxCol and whose // maximum row size is MaxRow and whose maximum // column size is MaxCol SparseMatrix Transpose(); // returns the SparseMatrix obtained by interchanging the // row and column value of every triple in *this

  39. 2.4 Sparse Matrices(Cont’) SparseMatrix Add(SparseMatrix b); // if the dimensions of a(*this) and b are the same, then // the matrix produced by adding corresponding items, // namely those with identical row and column values is // returned else error. SparseMatrix Multiply(SparseMatrix b); // if number of columns in a (*this) equals number of // rows in b then the matrix d produced by multiplying a // by b according to the formula // d[i][j]= (a[i][k]·b[k][j]), // where d[i][j] is the (i, j)th element, is returned. // k ranges from 0 to the number of columns in a-1 // else error. }; ADT 2.3 : Abstract data type SparseMatrix

  40. 2.4 Sparse Matrices(Cont’) 2.4.2 Sparse Matrix Representation • Representation • use the triple <row, col, value> to represent an element • store the triples by rows • for each row, the column indices are in ascending order • store the number of rows, columns, and nonzero elements

  41. 2.4 Sparse Matrices(Cont’) • C++ code class SparseMatrix; // forward declaration class MatrixTerm { friend class SparseMatrix private: int row, col, value; }; class SparseMatrix { private: int Rows, Cols, Terms; MatrixTerm smArray[MaxTerms]; public: SparseMatrix Transpose(); ... }

  42. 2.4 Sparse Matrices(Cont’) • Representation of the matrix of Figure 2.2(b) using smArray row col value row col value smArray[0] 0 0 15 smArray[0] 0 0 15 [1] 0 3 22 [1] 0 4 91 [2] 0 5 -15 [2] 1 1 11 [3] 1 1 11 [3] 2 1 3 [4] 1 2 3 [4] 2 5 28 [5] 2 3 -6 [5] 3 0 22 [6] 4 0 91 [6] 3 2 -6 [7] 5 2 28 [7] 5 0 -15 • (b) Figure 2.3 : Sparse matrix and its transpose stored as triples

  43. 2.4 Sparse Matrices(Cont’) 2.4.3 Transposing a Matrix • n element at [i][j] will be at [j][i] for (each row i) take element (i, j, value) and store it in (j, i, value) of the transpose; • Example • (0, 0, 15) → (0, 0, 15) • (0, 3, 22) → (3, 0, 22) • (0, 5, -15) → (5, 0, -15) • (1, 1, 11) → (1, 1, 11) • need to insert many new triples, elements are moved down very often • Find the elements in the order for (all elements in column j) place element (i, j, value) in position (j, i, value);

  44. 2.4 Sparse Matrices(Cont’) SparseMatrix SparseMatrix::Transpose() // return the transpose of a (*this) { SparseMatrix b; b.Rows = Cols; // rows in b = columns in a b.Cols = Rows; // columns in b = rows in a b.Terms = Terms; // terms in b = terms in a if (Terms > 0) // nonzero matrix { int CurrentB = 0; for (int c = 0; c < Cols; c++) // transpose by columns for (int i = 0; i < Terms; i++) // find elements in column c

  45. 2.4 Sparse Matrices(Cont’) if (smArray[i].col ==c) { b.smArray[CurrentB].row = c; b.smArray[CurrentB].col = smArray[i].row; b.smArray[CurrentB].value = smArray[i].value; CurrentB++; } } // end of if (Terms > 0) return b; } // end of transpose Program 2.10 : Transposing a matrix

  46. 2.4 Sparse Matrices(Cont’) • Analysis of transpose • the number of iterations of the for loop at line 12 is terms • the number of iterations of the for loop at line 11 is columns • total time is O(terms·columns) • total space is O(space for a and b) • Using two-dimensional arrays for(int j=0; j<columns; j++) for(int i=0; i<rows; i++) B[j][i]=A[i][j]; • total time is O(rows·columns)

  47. 2.4 Sparse Matrices(Cont’) • Comparison • O(terms·columns) =O(rows·columns2) > O(rows·columns) • space-time trade-off

  48. 2.4 Sparse Matrices(Cont’) • FastTranspose algorithm • determine the number of elements in each column of a → the number of elements in each row of b → starting point of each of b's rows • move elements of a one by one into their correct position in b • values for Figure 2.3 (b) matrix [0] [1] [2] [3] [4] [5] RowSize = 2 1 2 2 0 1 RowStart = 0 2 3 5 7 7

  49. 2.4 Sparse Matrices(Cont’) • asymptotic complexity • there are four loops O(columns+terms) • if terms → rows·columns, O(rows·columns) • if terms << rows·columns, less than O(rows·columns) • requires space for RowSize and RowStart

  50. 2.4 Sparse Matrices(Cont’) SparseMatrix SparseMatrix::FastTranspose() // The transpose of a (*this) is placed in b and is found in // O(terms+columns) time. { int *RowSize = new int[Cols]; int *RowStart = new int[Cols]; SparseMatrix b; b.Rows = Cols; b.Cols = Rows; b.Terms = Terms; if (Terms>0) // nonzero matrix { // compute RowSize[i] = number of terms in row i of b for (int i = 0; i<Cols; i++) RowSize[i] = 0; // initialize for (i = 0; i<Terms; i++) RowSize[smArray[i].col]++; // RowStart[i] = starting position of row i in b RowStart[0] = 0;

More Related