#06 More Structures LIFO FIFO. Contents. Queue vs. Stack 3. Stack Operations. Pop. Push. Stack Queue Hash table

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1 Contents #06 More Structures -07 FUNDAMENTAL PROGRAMMING I Stack Queue Hash table DEPARTMENT OF COMPUTER ENGINEERING, PSU v. Queue vs. Stack Stack Operations IN IN OUT Push: add an item to the top Pop: remove the item at the top and return : copy the item at the top OUT First-In First-Out FIFO Last-In First-Out LIFO Push 5 Pop 6 Add an item at the top After the push, the new item becomes the top The stack is an overflow state if there is no room for the new item Remove the item at the top and return it to the user The next older item becomes new top When the last item in the stack is deleted, it must be set to its empty state If pop is called when the stack is empty, then it is in an underflow state Before: push After: push Before: Pop After: Pop

2 Stack Implementations 7 Stack Implementations 8 Using array Easy but not resizable Initialize stack with specified capacity and cursor= 0 Push: append data at the end, increase cursor Pop: remove data at the end, decrease cursor Raise stack overflow when push with cursor = capacity Raise stack underflow when pop with cursor = 0 struct stack{ int *datas; int capacity; int cursor; typedef struct stack Stack; Using linked-list Difficult but resizable Initialize stack with given capacity head = NULL, size = 0 Push: insert given node at the head of linked list Pop: remove the node at the head of linked list Increase capacity when needed Decrease capacity lower than size should be handled carefully. struct node{ int *data; struct node *next; struct stack{ struct node *head; int size; int capacity; typedef struct stack Stack; Case Study 9 Case Study: init 0 Stack *stack_init(int capacity); void stack_push(stack *stack, int data); int stack_pop(stack *stack); int stack_is_empty(stack *stack); void stack_free(stack **sptr); int main(){ Stack *s = stack_init(0); stack_push(s, ); stack_push(s, 7); stack_push(s, ); while(!stack_is_empty(s)){ printf("%d\n", stack_pop(s)); Stack *stack_init(int capacity){ Stack *s = NULL; if(capacity <= 0) return NULL; s = (Stack*)malloc(sizeof(Stack)); s->datas = malloc(sizeof(int) * capacity); s->capacity = capacity; s->cursor = 0; return s; stack_free(&s); return 0; Case Study: push, pop Case Study: empty?, free void stack_push(stack *stack, int data){ if(stack->cursor >= stack->capacity){ fprintf(stderr, "stack overflow\n"); return; stack->datas[stack->cursor] = data; stack->cursor++; int stack_pop(stack *stack){ int d = 0; if(stack->cursor <= 0){ fprintf(stderr, "stack underflow\n"); return 0; d = stack->datas[stack->cursor - ]; stack->cursor--; return d; int stack_is_empty(stack *stack){ return (stack == NULL stack->cursor == 0)? : 0; void stack_free(stack **sptr){ Stack *s = *sptr; free(s->datas); free(s); *sptr = NULL;

3 Stack Applications Case Study: Decimal Binary Reversing Data (see earlier Case Study) 7 5 => 5 7 Converting Decimal to Binary => 0 Converting Infix to Postfix ( + ) * 8 => + 8 * Postfix Evaluation * 5 + => 7 scanf("%d", &number); while(number > 0){ digit = number % ; stack_push(s, digit); number = number / ; while(!stack_is_empty(s)){ printf("%d", stack_pop(s)); printf("\n"); Case Study: Postfix Evaluation 5 Case Study: Postfix Evaluation 6 To evaluate a postfix expression, execute the Example: evaluate " * 5 +" following steps until the end of the expression.. If current input is an operand, push it on the stack.. If current input is an operator, pop its two operands, apply the operator, and push the result onto the stack At the end of input, the value of the postfix expression is on the top of the stack. Queue Operations 7 8 Like check-out lines in a store, a queue has a front and a rear. Enqueue: insert an element at the rear of the queue Dequeue: remove an element from the front of the queue Remove (Dequeue) front rear Insert (Enqueue) Hash Tables Modified version of Presentation from Addison Wesley Longman, For use with Data Structures and Other Objects Using C++ by Michael Main and Walter Savitch.

What is a Hash Table? 9 What is a Hash Table? 0 The simplest kind of hash table is an array of records. This example has 70 records. Each record has a special field, called its key.

4 What is a Hash Table? 9 What is a Hash Table? 0 The simplest kind of hash table is an array of records. This example has 70 records. Each record has a special field, called its key. In this example, the key is a long integer field called Number. The number might be a person's identification number, and the rest of the record has information about the person. When a hash table is in use, some spots contain valid records, and other spots are "empty". [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] An array of records Number 8990 Inserting a New Record Inserting a New Record In order to insert a new record, the key must somehow be converted to an array index. The index is called the hash value of the key. Number Typical way create a hash value: Number % % 70 = The hash value is used for the location of the new record. Number [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] Number 8990 Number 8990 Number Collisions Searching for a Key Here is another new record to insert, with a hash value of. This is called a collision, because there is already another valid record at []. When a collision occurs, move forward until you find an empty spot. The record goes to empty spot. Number My hash value is []. The data that's attached to a key can be found fairly quickly. Calculate the hash value. Check that location of the array for the key. Keep moving forward until you find the key, or you reach an empty spot. When the item is found, the information can be copied to the necessary location. [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] Number 8990 Number Number 8990 Number Number

Deleting a Record 5 Deleting a Record 6 Records may also be deleted from a hash table. But the location must not be left as an ordinary "empty spot" since that could interfere with searches.

5 Deleting a Record 5 Deleting a Record 6 Records may also be deleted from a hash table. But the location must not be left as an ordinary "empty spot" since that could interfere with searches. The location must be marked in some special way so that a search can tell that the spot used to have something in it. Please delete me! [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] [ 0 ] [ ] [ ] [ ] [ ] [ 5 ] [ 700] Number 8990 Number Number Number 8990 Number Number

Stacks and Queues. Stack - Abstract Data Type. Stack Applications. Stack - Abstract Data Type - C Interface

Stacks and Queues. Stack - Abstract Data Type. Stack Applications. Stack - Abstract Data Type - C Interface Stacks and Queues Stack - Abstract Data Type. Stacks and queues ubiquitous -structure in computing. Part of many important algorithms. Good example of abstract types. Good example to practice programming