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infsci 0015 - data structures lecture 23: stack again - linked-list implementation

Stack is an Abstract Data Type. We do not care about implementationWe can use a stack calling key functionsCreatePushPopStack TopFull?Empty?. Multiple implementations. An ADT can have several implementationsImplementations may be different, but implementation details are hiddenInterface functions are the sameApplication programs will not see any difference.

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infsci 0015 - data structures lecture 23: stack again - linked-list implementation

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    1. INFSCI 0015 - Data Structures Lecture 23: Stack Again - Linked-List Implementation Peter Brusilovsky http://www2.sis.pitt.edu/~peterb/0015-011/

    4. Multiple implementations An ADT can have several implementations Implementations may be different, but implementation details are hidden Interface functions are the same Application programs will not see any difference

    5. Why linked list implementation? Need to understand the concept of an abstract data type (see slide above) Need to see nested implementations Need to have more practice with dynamic data structures Need to see some application of LLs Every Data Structure course does it

    9. Key Structures in C typedef struct node { int data ; struct node *link ; } STACK_NODE; typedef struct stack { int count ; STACK_NODE *top ; } STACK;

    10. createStack: C code static STACK *createStack (int par) /* dummy par */ { STACK *stack ; stack = (STACK *) malloc( sizeof (STACK) ) ; if (stack) { stack->top = NULL ; stack->count = 0; } /* if */ return stack ; } /* createStack */

    12. stackPush: C code static int pushStack(STACK *stack, int dataIn) { STACK_NODE *newPtr; newPtr = (STACK_NODE *) malloc(sizeof( STACK_NODE)); if (newPtr == NULL) return 0; /* no more space */ newPtr->data = dataIn; newPtr->link = stack->top; stack->top = newPtr; ( stack->count )++; return 1; } /* pushStack */

    14. popStack: C code static int popStack (STACK *stack, int *dataOutPtr) { STACK_NODE *dltPtr; if (stack->count == 0) return 0; else { dltPtr = stack->top; *dataOutPtr = (stack->top)->data; stack->top = (stack->top)->link; free (dltPtr); (stack->count)--; } /* else */ return 1; } /* popStack */

    15. stackTop static int stackTop (STACK *stack, int *dataOutPtr) { if (stack->count > 0) { *dataOutPtr = (stack->top)->data; return 1; } else return 0; } /* stackTop */

    16. emptyStack and stackCount static int emptyStack (STACK *stack) { return (stack->count == 0); } /* emptyStack */ static int stackCount(STACK *stack) { return stack->count; } /* stackCount */

    17. fullStack static int fullStack (STACK *stack) { STACK_NODE *temp; if ( (temp = (STACK_NODE *)malloc (sizeof (STACK_NODE))) ) { free ( temp ); return 0; } /* if */ /* malloc failed */ return 1; } /* fullStack */

    18. destroyStack static STACK *destroyStack ( STACK *stack ) { STACK_NODE *deletePtr; if (stack) { /* Delete all nodes in stack */ while ( stack->top != NULL ) { deletePtr = stack->top ; stack->top = stack->top->link; free ( deletePtr ); } /* while */ /* Stack now empty. Destroy stack head node. */ free (stack); } /* if stack */ return NULL; } /* destroyStack */

    20. Abstract Data Types We know a conceptual idea of a data type We can work with objects of this type by using a set of predefined operations We do not really care (and know) how it is implemented Implementation can be changed - not even a bit in the application program will be changed Different implementations are possible (could be used in different cases)

    21. Stack and Queue are ADTs There are many others classic ADTs We will learn: Lists Trees Abstract Data Types

    22. Compare implementations Array implementation LL implementation

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