Transcript CS200 - Data Structures

CS2006 - Data Structures I
Chapter 7
Stacks II
Topics
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Implementation of ADT Stack
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2
Using Linked lists
Using ADT List
Linked List Stack
Implementation
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Stacks can grow and shrink dynamically
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No particular linked list variations are required:
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3
The head pointer can also serve as the top of the
stack.
Pushing becomes inserting the first node in a linked
list.
Popping becomes removing the first node.
Linked List Stack
Implementation
The head of List is the top of the stack
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head
1
top
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7
1
3
7
9
4
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LL Stack Implementation
// Assumes that the classes StackInterface and Node are available
public class StackRefereenceBased implements StackInterface {
private Node top;
// class Node is the same used in the LinkedList class except it stores
// Objects rather than Comparables
public StackRefereenceBased (){
top = null;
} // end default constructor
public boolean isEmpty() {
return (top == null);
} // end isEmpty
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LL Stack Implementation
// Assumes that the classes StackInterface and Node are available
public class StackRefereenceBased implements StackInterface {
private Node top;
// class Node is the same used in the LinkedList class except it stores
// Objects rather than Comparables
public StackRefereenceBased (){
top = null;
} // end default constructor
public boolean isEmpty() {
return (top == null);
} // end isEmpty
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LL Stack Implementation (2)
public void push(Object newItem) {
top = new Node(newItem, top);
} // end push
public Object pop() throws StackException {
if (!isEmpty()) {
Object temp = top.getItem();
top = top.getNext();
return temp;
}
else {
throw new StackException("StackException on " + "pop: stack empty");
} // end if
} // end pop
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LL Stack Implementation (2)
public void push(Object newItem) {
top = new Node(newItem, top);
} // end push
public Object pop() throws StackException {
if (!isEmpty()) {
Object temp = top.getItem();
top = top.getNext();
return temp;
}
else {
throw new StackException("StackException on " + "pop: stack empty");
} // end if
} // end pop
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LL Stack Implementation (3)
public void popAll() {
top=null;
} // end popAll
public Object peek() throws StackException {
if (!isEmpty()) {
return top.getItem();
}
else {
throw new StackException("StackException on " +
"peek: stack empty");
} // end else
} // end peek
} // end StackReferencedBased
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LL Stack Implementation (3)
public void popAll() {
top=null;
} // end popAll
public Object peek() throws StackException {
if (!isEmpty()) {
return top.getItem();
}
else {
throw new StackException("StackException on " +
"peek: stack empty");
} // end else
} // end peek
} // end StackReferencedBased
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ADT Stack ADT List Implementation
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All stack operations can be implemented
using the ADT List's operations
The implementation is simpler to write
than the array-based and makes used of
previously-written code (code reuse)
Position 1 of the list represents the top
position of the stack
ADT Stack ADT List Implementation
List position 1
10
2
80
3
60
List site()
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.
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5
top
ADT List Stack Implementation
// Assumes that the classes ListInterface and Node are available
public class StackListBased implements StackInterface {
private ListInterface list;
public StackListBased() {
list = new ListReferenceBased();
} // end default constructor
public boolean isEmpty() {
return list.isEmpty ();
} // end isEmpty
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ADT List Stack Implementation
// Assumes that the classes ListInterface and Node are available
public class StackListBased implements StackInterface {
private ListInterface list;
public StackListBased() {
list = new ListReferenceBased();
} // end default constructor
public boolean isEmpty() {
return list.isEmpty ();
} // end isEmpty
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List Stack Implementation (2)
public void push(Object newItem) {
list.add (1, newItem);
} // end push
public Object pop() throws StackException {
if (!list.isEmpty()) {
Object temp = list.get(1);
list.remove(1);
return temp;
}
else {
throw new StackException("StackException on " + "pop: stack empty");
} // end if
} // end pop
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List Stack Implementation (2)
public void push(Object newItem) {
list.add (1, newItem);
} // end push
public Object pop() throws StackException {
if (!list.isEmpty()) {
Object temp = list.get(1);
list.remove(1);
return temp;
}
else {
throw new StackException("StackException on " + "pop: stack empty");
} // end if
} // end pop
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List Stack Implementation (3)
public void popAll() {
list.removeAll();
} // end popAll
public Object peek() throws StackException {
if (!list.isEmpty()) {
return list.get(1);
}
else {
throw new StackException("StackException on " +
"peek: stack empty");
} // end else
} // end peek
} // end StackListBased
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ADT Stack Implementation Comparison
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Array-Based
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LL-Based
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More complicated than ADT List
Most flexible, No size restrictions
ADT List-Based
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No overhead of reference manipulation
Prevents adding elements if the array is full
Simpler to write
Not as efficient as using a linked list directly
Review
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The ______ method of the ADT stack
retrieves and then removes the top of the
stack.
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createStack
push
pop
peek
Review
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The ______ method of the ADT stack
retrieves the top of the stack, but does not
change the stack.
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createStack
push
pop
peek
Review
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Which of the following methods of the ADT
stack accepts a parameter?
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push
pop
createStack
peek
Review
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If a stack is used by an algorithm to check
for balanced braces, which of the following
is true once the end of the string is
reached?
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the stack is empty
the stack has one “{”
the stack has one “}”
the stack has one “{” and one “}”
Review
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Which of the following operations of the
ADT stack does not throw a
StackException?
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push
pop
popAll
peek
Review
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The pop operation throws a
StackException when it tries to ______.
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add an item to an empty stack
add an item to an array-based implementation
of a stack that is already full
delete an item from an array-based
implementation of a stack that is already full
delete an item from an empty stack
Review
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The push operation throws a
StackException when it tries to ______.
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add an item to an empty stack
add an item to an array-based implementation
of a stack that is already full
delete an item from an array-based
implementation of a stack that is already full
delete an item from an empty stack
Review
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In the StackInterface class, the pop
method returns an item that is an instance
of ______.
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Integer
Double
String
Object