3 adt unsorted list. list definitions linear relationship each element except the first has a unique...
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3ADT Unsorted List
List Definitions
Linear relationship Each element except the first has a unique predecessor, and each element except the last has a unique successor.
Length The number of items in a list; the length can vary over time.
List Definitions
Unsorted list A list in which data items are placed in no particular order; the only relationship between data elements is the list predecessor and successor relationships.
Sorted list A list that is sorted by the value in the key; there is a semantic relationship among the keys of the items in the list.
Key The attributes that are used to determine the logical order of the list.
Abstract Data Type (ADT)
• A data type whose properties (domain and operations) are specified independently of any particular implementation.
What
How
• Application (or user) level: modeling real-life data in a specific context.
• Logical (or ADT) level: abstract view of the domain and operations.
• Implementation level: specific representation of the structure to hold the data items, and the coding for operations.
Data from 3 different levels
Sorted and Unsorted Lists
UNSORTED LIST
Elements are placed into the list in no particular order.
SORTED LIST
List elements are in an order that is sorted in some way -- either numerically or alphabetically by the elements themselves, or by a component of the element (called a KEY member) .
Unsorted List ADT Operations
• Constructor: Called when an instance of this data type is created.
• Transformers: MakeEmpty, PutItem, and DeleteItem
• Observer: IsFull, GetLength, GetItem• Iterator: ResetList, GetNextItem
ADT Unsorted List Operations
Transformers • MakeEmpty • PutItem • DeleteItem
Observers • IsFull• GetLength
• GetItem
Iterators • ResetList • GetNextItem
change state
observe state
process all
What is a Generic Data Type?
A generic data type is a type for which the operations are defined but the types of the items being manipulated are not defined.
One way to simulate such a type for our UnsortedList ADT is via a user-defined class ItemType with member function ComparedTo returning an enumerated type value LESS, GREATER, or EQUAL.
// SPECIFICATION FILE ( unsorted.h )#include “ItemType.h”
class UnsortedType // declares a class data type{public : // 8 public member functions void UnsortedType ( ); bool IsFull ( ) const; int GetLength ( ) const ; // returns length of list ItemType GetItem ( ItemType item, bool& found); void PutItem ( ItemType item ); void DeleteItem ( ItemType item ); void ResetList ( ); ItemType GetNextItem ();
private : // 3 private data members int length; ItemType info[MAX_ITEMS]; int currentPos;};
Class Constructor
A special member function of a class
that is implicitly invoked when a class
object is defined.
Class Constructor Rules
1 A constructor cannot return a function value, and has no return value type.
2 A class may have several constructors. The compiler chooses the appropriate constructor by the number and types of parameters used.
3 Constructor parameters are placed in a parameter list in the declaration of the class object.
4 The parameterless constructor is the default constructor.
5 If a class has at least one constructor, and an array of class objects is declared, then one of the constructors must be the default constructor, which is invoked for each element in the array.
Class Interface Diagram
UnsortedType class
IsFull
GetLength
ResetList
DeleteItem
PutItem
UnsortedType
GetItem
GetNextItem
Private data:
length
info [ 0 ] [ 1 ] [ 2 ]
[MAX_ITEMS-1]
currentPos
14
// IMPLEMENTATION FILE ARRAY-BASED LIST ( unsorted.cpp )#include “itemtype.h”
void UnsortedType::UnsortedType ( ) // Pre: None.// Post: List is empty.{
length = 0;}
void UnsortedType::InsertItem ( ItemType item )// Pre: List has been initialized. List is not full. // item is not in list.// Post: item is in the list.{
info[length] = item;length++;
}
Before Inserting Hsing into anUnsorted List
length 3
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] .
. .
[MAX_ITEMS-1]
The item willbe placed intothe length location,and length will beincremented.
After Inserting Hsing into anUnsorted List
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. . [MAX_ITEMS-1]
17
int UnsortedType::GetLength( ) const// Pre: List has been inititalized.// Post: Function value == ( number of elements in// list ).{
return length; }
bool UnsortedType::IsFull ( ) const// Pre: List has been initialized.// Post: Function value == ( list is full ).{
return ( length == MAX_ITEMS );}
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ItemType UnsortedType::GetItem ( ItemType item, bool& found ) // Pre: Key member of item is initialized.// Post: If found, item’s key matches an element’s key in the list// and a copy of that element is returned; // otherwise, input item is returned.{ bool moreToSearch; int location = 0;
found = false;moreToSearch = ( location < length );while ( moreToSearch && !found ){ switch ( item.ComparedTo( info[location] ) )
{ case LESS : case GREATER : location++;
moreToSearch = ( location < length ); break;
case EQUAL : found = true; item = info[ location ];
break; } } return item}
Getting Ivan from an Unsorted List
moreToSearch: true
found: false
location: 0
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
.
[MAX_ITEMS-1]
Getting Ivan from an Unsorted List
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
.
[MAX_ITEMS-1]
moreToSearch: true
found: false
location: 1
Getting Ivan from an Unsorted List
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
moreToSearch: true
found: false
location: 2
Getting Ivan from an Unsorted List
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
moreToSearch: true
found: false
location: 3
Getting Ivan from an Unsorted List
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
moreToSearch: false
found: false
location: 4
void UnsortedType::DeleteItem ( ItemType item ) // Pre: item’s key has been inititalized.// An element in the list has a key that matches item’s.// Post: No element in the list has a key that matches item’s.{
int location = 0 ; while (item.ComparedTo (info [location] ) != EQUAL )
location++;
// move last element into position where item was located
info [location] = info [length - 1 ] ;length-- ;
}
Deleting Bradley from an Unsorted List
location: 0 length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
Key Bradley hasnot been matched.
Deleting Bradley from an Unsorted List
location: 1
Key Bradley hasbeen matched.
length 4
info [ 0 ] Maxwell
[ 1 ] Bradley
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
Deleting Bradley from an Unsorted List
location: 1
length 4
info [ 0 ] Maxwell
[ 1 ] Hsing
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
Placed copy oflast list elementinto the position where the key Bradley was before.
Deleting Bradley from anUnsorted List
location: 1
length 3
info [ 0 ] Maxwell
[ 1 ] Hsing
[ 2 ] Asad
[ 3 ] Hsing .
. .
[MAX_ITEMS-1]
Decremented length.
void UnsortedType::ResetList ( )
// Pre: List has been inititalized.
// Post: Current position is prior to first element in list.
{
currentPos = -1;
}
ItemType UnsortedType::GetNextItem ()
// Pre: List has been initialized. Current position is defined.
// Element at current position is not last in list.
// Post: Current position is updated to next position.
// item is a copy of element at current position.
{
currentPos++;
item = info [currentPos];
}
// SPECIFICATION FILE ( itemtype.h )
const int MAX_ITEM = 5 ;enum RelationType { LESS, EQUAL, GREATER };
class ItemType // declares class data type{public : // 3 public member functions
RelationType ComparedTo ( ItemType ) const; void Print ( ) const;
void Initialize ( int number ) ;
private : // 1 private data memberint value ; // could be any different
// type, including a class} ;
Specifying class ItemType
// IMPLEMENTATION FILE ( itemtype.cpp )// Implementation depends on the data type of value.
#include “itemtype.h”#include <iostream>
RelationType Itemtype::ComparedTo(ItemType otherItem) const
{if ( value < otherItem.value )
return LESS;else if ( value > otherItem.value )
return GREATER;else return EQUAL;
} void ItemType::Print ( ) const {
using namespace std;cout << value << endl;
}void ItemType::Initialize ( int number ){
value = number; }
Private data
value
ComparedTo
Initialize
class ItemType
ItemType Class Interface Diagram
What is a pointer variable?• A pointer variable is a variable whose value is the address of a
location in memory.
• To declare a pointer variable, you must specify the type of value that the pointer will point to. For example,
int* ptr; // ptr will hold the address of an int
char* q; // q will hold the address of a char
Using a pointer variable
int x; x = 12;
int* ptr; ptr = &x;
NOTE: Because ptr holds the address of x, we say that ptr “points to” x
2000
12
x
3000
2000
ptr
2000
12
x
3000
2000
ptr
int x; x = 12;
int* ptr; ptr = &x;
std::cout << *ptr;
NOTE: The value pointed to by ptr is denoted by *ptr
Unary operator * is the deference (indirection) operator
int x; x = 12;
int* ptr; ptr = &x;
*ptr = 5; // changes the value // at address ptr to 5
Using the dereference operator
2000
12 5
x
3000
2000
ptr
char ch;
ch = ‘A’;
char* q; q = &ch;
*q = ‘Z’;
char* p; p = q; // the right side has value 4000
// now p and q both point to ch
Another Example
4000
A Z
ch
5000 6000
4000 4000
q p
38
C++ Data Types
Structured
array struct union class
Address
pointer reference
Simple
Integral Floating
char short int long enum
float double long double
2000
ptr
Dynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
std::cout << *ptr;
New is an operator
Dynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
std::cout << *ptr;
NOTE: Dynamic data has no variable name
2000
ptr
Dynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
std::cout << *ptr;
2000
ptr
‘B’
Dynamically Allocated Data
char* ptr;
ptr = new char;
*ptr = ‘B’;
std::cout << *ptr;
delete ptr;
2000
ptr
NOTE: Delete deallocates the memory pointed to by ptr.
?
Yes, but what does new do?
New
• takes a pointer variable,
• allocates memory for it to point, and
• leaves the address of the assigned memory in the pointer variable.
• If there is no more memory, the pointer variable is set to NULL.
The NULL PointerThere is a pointer constant called NULL
available in cstddef.
NULL is not a memory address; it means that the pointer variable points to nothing.
It is an error to dereference a pointer whose value is NULL. It is the programmer’s job to check for this.
while (ptr != NULL) { . . . // ok to use *ptr here
}
The object or array currently pointed to by the pointer is deallocated, and the pointer is considered unassigned. The memory is returned to the free store.
Square brackets are used with delete to deallocate a dynamically allocated array of classes.
Using operator delete
int* ptr = new int; *ptr = 3;
ptr = new int; // changes value of ptr *ptr = 4;
What happens here?
3
ptr
3
ptr
4
Memory Leak
A memory leak occurs when dynamic memory (that was created using operator new) has been left without a pointer to it by the programmer, and so is inaccessible.
int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5;
8
ptr
-5
ptr2
How else can an object become inaccessible?
Causing a Memory Leak
int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
ptr = ptr2; // here the 8 becomes inaccessible
8
ptr
-5
ptr2
8
ptr
-5
ptr2
• occurs when two pointers point to the same object and delete is applied to one of them.
int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
ptr = ptr2;
A Dangling Pointer
8
ptr
-5
ptr2
FOR EXAMPLE,
int* ptr = new int;
*ptr = 8;
int* ptr2 = new int;
*ptr2 = -5;
ptr = ptr2;
delete ptr2; // ptr is left dangling
ptr2 = NULL;
Leaving a Dangling Pointer
8
ptr
-5
ptr2
8
ptr
NULL
ptr2
Remember?
• A list is a homogeneous collection of elements, with a linear relationship between elements.
• That is, each list element (except the first) has a unique predecessor, and each element (except the last) has a unique successor.
ADT Unsorted List Operations
Transformers • MakeEmpty • PutItem • DeleteItem
Observers • IsFull• GetLength
• GetItem
Iterators • ResetList • GetNextItem
change state
observe state
process all
53
#include “ItemType.h” // unsorted.h . . .class UnsortedType{public : // LINKED LIST IMPLEMENTATION
// The public interface is the same
private : // The private part is different
NodeType<ItemType>* listData;int length;NodeType<ItemType>* currentPos;
};
Do we have to keep a length field?Do we need an IsFull?
class UnsortedType<char>
MakeEmpty
~UnsortedType
DeleteItem . . .
PutItem
UnsortedType
GetItem
GetNextItem
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
55
// LINKED LIST IMPLEMENTATION ( unsorted.cpp )#include “itemtype.h”
UnsortedType::UnsortedType ( ) // constructor// Pre: None.// Post: List is empty.{
length = 0;listData = NULL;
}
int UnsortedType::GetLength( ) const// Post: Function value = number of items in the list.{
return length;}
56
ItemType UnsortedType::GetItem( ItemType item, bool& found ) // Pre: Key member of item is initialized.// Post: If found, item’s key matches an element’s key in the list // a copy of that element is returned; otherwise,// origianl item is returned.{ bool moreToSearch;
NodeType<ItemType>* location; location = listData;
found = false ;moreToSearch = ( location != NULL );while ( moreToSearch && !found ) { if ( item == location->info ) // match here
{ found = true; item = location->info;
} else // advance pointer { location = location->next;
moreToSearch = ( location != NULL ); }
} return item; }
57
void UnsortedType::PutItem ( ItemType item )
// Pre: list is not full and item is not in list.
// Post: item is in the list; length has been incremented.
{
NodeType<ItemType>* location;
// obtain and fill a node
location = new NodeType<ItemType>;
location->info = item;
location->next = listData;
listData = location;
length++;
}
Inserting ‘B’ into an Unsorted List
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
location = new NodeType;
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
item
location
‘B’
location->info = item ;
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
item
location
‘B’
‘B’
location->next = listData ;
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
item
location
‘B’
‘B’
listData = location ;
‘X’ ‘C’ ‘L’
Private data:
length 3
listData
currentPos ?
item
location
‘B’
‘B’
length++ ;
‘X’ ‘C’ ‘L’
Private data:
length 4
listData
currentPos ?
item
location
‘B’
‘B’
Comparing List Implementations
• The array list implementation appends items at the end of the list. For example, after 5 insertions, the list is 56791.
• The linked list implementation appends items from the head of the list. After 5 insertions, the list is 19765
• Insertions would be O(1) for both when placing the items in the easiest places; otherwise, insertions would take O(N) for array implementation, if items must be inserted at the head of the list.
• Deletions take O(N) for both list implementations.• MakeEmpty takes O(N) to delete nodes in the linked
list, and O(1) for array to set the length to 0.
Workout
• Compare the storage space requirements of array-based vs. linked list based implementations for the following data:• Maximum of 200 80-byte strings• Maximum of 200 2-byte integers• Maximum of 200 12-byte structs
• Integer indices require 2-bytes; pointers require 4-bytes
• Graph storage requirements for both implementation approaches, as the number of elements in the structure ranges from 0 to the maximum structure size