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Data Structures (Second Part) Lecture 3 : Array, Linked List, Stack & Queue Bong-Soo Sohn Assistant Professor School of Computer Science and Engineering Chung-Ang University

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ADT (Abstract Data Type) ADT specification of a set of data and the set of operations that can be performed on the data ADT is abstract : independent of concrete implementations can be thought as an interface (hidden from implementation) In OOP, ADT is a class. Instance of ADT is an object. C style ADT long stack_create(); /* create new instance of a stack */ void stack_push(long stack, void *item); /* push an item on the stack */ void *stack_pop(long stack); /* get item from top of stack */ void stack_delete(long stack); /* delete the stack */ long stack; struct foo *f; stack = stack_create(); /* create a stack */ stack_push(stack, f); /* add foo structure to stack */ f = stack_pop(stack); /* get top structure from stack */

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Array ADT Array is a consecutive set of memory locations. Array ADT is a more general structure Structure Array is objects : A set of pairs where for each value from the set item. Index is a finite ordered set of one or more dimensions functions : for all A ∈ Array; i ∈ index; x ∈ item; j; size 2 integer Array Create(j, list) ::= Array Retrieve(A, i) ::= Array Store(A, i, x) ::= end Array

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Arrays in C int list[5], *plist[5] v Implementation variableMemory Address list[0] (= base address) list[1] + sizeof(int) list[2] + 2 sizeof(int) list[3] + 3 sizeof(int) list[4] + 4 sizeof(int) 5 pointers to integers from plist[0] to plist[4] 5 integers from list[0] to list[4]

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Structure collections of data of the different types typedef struct PERSON { char name[10]; int age; float salary; } PERSON person;

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Using Pointers Set all pointers to NULL when they are not actually pointing to an object p = NULL *p NULL? A value in location zero? Explicit type casting pi = malloc(sizeof (int)); pf = (float *) pi;

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Heap malloc free Garbage int *pi; pi = (int *)mlloc (sizeof (int)); *pi = 1; pi = (int *) malloc ( sizeof (int)); *pi = 2; 1 2 pi garbage

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Garbage Automatic garbage collection Memory Leak Dangling Pointer

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Singly Linked Lists a1a1 ptr a2a2 anan typedef struct list_node *list_pointer; typedef struct list_node { char data[data]; list_pointer link; }; list_pointer ptr = NULL; /* create a null list */

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Necessary capabilities for linked representations. A mechanism for defining a node’s structure : self-referential structure A way to create new nodes : malloc A way to remove nodes : free

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o Create a new node ptr ptr = (list_pointer)malloc(sizeof(struct list_node)); o Assign a value to a field in the node. strcpy (ptr data, “bat”) ; ptr link = NULL; (ptr link) (*ptr).link In general, e (*e) ptr

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Insertion (after node q) q p x (1) (1) p = (list_pointer) malloc ( sizeof (struct list_node)); p data = x; (2) (2) p link = q link; (3) (3) q link = p;

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Deletion (after node q) (2) (2) q link = (q link) link; q (1) p = q link; p (1) (3) (3) free (p);

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Stack An ordered list in which insertions and deletions are made at one end called top. LIFO (Last-In-First-Out) Operations Create IsEmpty IsFull Push Pop

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Implementation of Stack using Array Stack CreateS ( max stack size ) ::= #define MAX STACK SIZE 100 typedef struct { int key ; /* other fields */ } element ; element stack[MAX STACK SIZE] ; int top = –1; Boolean IsEmpty ( stack ) ::= top 0 Boolean IsFull ( stack ) ::= top MAX_STACK_SIZE – 1

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Stack Add ( stack, item ) ::= void add ( int *top, element item ) /* push */ { if ( *top MAX_STACK_SIZE – 1 ) { stack_full() ; return ; } stack[++*top] := item ; } Element Delete ( stack ) ::= element delete ( int *top ) /* pop */ { if ( *top < 0 ) return stack_empty() ; return stack[(*top) – – ]; }

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Queue An ordered list in which all insertions take place at one end and all deletions take place at the opposite end. Q = (a 0,, a n-1 ) front element o FIFO ( First-In-First-Out ) rear element

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Implementation using Array. Queue CreateQ ( max_queue_size ) ::= #define MAX_QUEUE_SIZE 100 typedef struct { int key ; /* other fields */ } element ; element queue[MAX_QUEUE_SIZE] ; int rear = – 1 ; int front = – 1 ; Boolean IsEmptyQ ( queue ) ::= front == rear Boolean IsFullQ ( queue ) ::= rear == MAX_QUEUE_SIZE – 1

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Queue AddQ ( queue, item ) ::= void addq ( int *rear, element item ) { if ( *rear = = MAX_QUEUE_SIZE – 1 ) { queue_full() ; return ; } queue[++*rear] = item ; } Element DeleteQ (queue ) ::= element deleteq ( int *front, int rear ) { if ( *front = = rear ) return queue_empty() ; return queue[++*front] ; }

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*A problem in the above implementation frontQ[0] Q[1] Q[2] Q[4]comments –1 0 1 2 J 1 J 1 J 2 J 1 J 2 J 3 J 2 J 3 J 3 J 3 J 4 J 4 empty queue addq J 1 addq J 2 addq J 3 delq J 1 delq J 2 delq J 4 delq J 3 rear –1 0 1 2 3 The queue gradually shifts to the right

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Circular queue implementation Regard the array as circular. Initially front = rear = 0 A circular queue is empty if front == rear before deletion A circular queue is full if front == rear after insertion A circular queue holds at most MAX_QUEUE_SIZE - 1 elements

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void addq ( int front, int *rear, element item ) { if ( *rear == MAX_QUEUE_SIZE ) *rear == 0; else (*rear)++ ; if (front == *rear) { queue_full() ; return; } queue[*rear] = item ; } element deleteq ( int *front, int rear) { if ( *front == rear ) return queue_empty () ; *front = ( *front + 1) % MAX_QUEUE_SIZE ; return queue[*front] ; } *rear = (*rear+1) % MAX_QUEUE_SIZE

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