1. Stacks

2. Data Structure: Stacks
Outline
Linked-list Implementation
Array Implementation
Applications
4/26/2019
Data Structure: Stacks

3. Data Structure: Stacks
Stack ADT 2
List A1, A2, …, AN
If N=0, it is an empty stack.
Methods
Push: add the element on the top of stack
Pop: take the element from the top of stack
Top: read the element on the top of stack
pop
push
topOfStack 7 1 8 3 4
4/26/2019
Data Structure: Stacks

4. Linked-list Implementation
public class StackLi
{ public StackLi()
{ topOfStack=null; }
public boolean isFull()
{ return false; }
public void makeEmpty()
{ topOfStack=null; }
...
private ListNode topOfStack; } A5
topOfStack A4 A3 A2 A1
4/26/2019
Data Structure: Stacks

5. Data Structure: Stacks
Method push, pop, top
public void push(object x)
{ topOfStack = new ListNode(x, topOfStack); }
public void pop() throws Underflow
{ if (isEmpty()) throw new Underflow();
topOfStack = topOfStack.next;
public Object top()
{ if (isEmpty()) return null;
return topOfStack.element;
4/26/2019
Data Structure: Stacks

6. Data Structure: Stacks
Method topAndPop
public Object topAndPop()
{ if (isEmpty()) return null;
Object topItem = topOfStack.element;
topOfStack = topOfStack.next;
return topItem; }
4/26/2019
Data Structure: Stacks

7. Data Structure: Stacks
Array Implementation
public class StackAr
{ public StackAr()
{ this(DEFAULT_SIZE); }
public StackAr(int size)
{ theArray = new Object [size];
topOfStack=-1;}
public boolean isEmpty()
{ return topOfStack==-1; }
public boolean isFull()
{ return topOfStack==
theArray.length-1;}
...
private Object [] theArray;
private int topOfStack;
static final int DEFAULT_SIZE=10; } 6 5 A6 4 A5 3 A4 2 A3 1 A2 A1
topOfStack=5
4/26/2019
Data Structure: Stacks

8. Data Structure: Stacks
Method push, pop, top
public void push(object x) throws Overflow
{ if (isFull())throw new Overflow();
theArray[++topOfStack] = x; }
public void pop() throws Underflow
{ if (isEmpty()) throw new Underflow();
theArray[topOfStack--] = null;
public Object top()
{ if (isEmpty()) return null;
return theArray[topOfStack];
4/26/2019
Data Structure: Stacks

9. Data Structure: Stacks
Method topAndPop
public Object topAndPop()
{ if (isEmpty()) return null;
Object topItem = theArray[topOfStack];
theArray[topOfStack--] = null;
return topItem; }
4/26/2019
Data Structure: Stacks

10. Application:Balancing Parenthesis
( ( ( ) ( ) ( ( ) ( ) ) ) ( ) )
StackLi symStk=new StackLi;
Object sym=nextsym();
while (sym!=null)
{ if (sym.isOpenPar())
symStk.push(sym);
if (sym.isClsPar())
if (!symStk.isEmpty())
symStk.pop();
else return false;
sym=nextsym(); }
return symStk.isEmpty(); ( ( ( (
4/26/2019
Data Structure: Stacks