STACK ADT

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STACK ADT

• Department of Computer Science
• Xavier University

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Definition

• container of objects that are inserted and
  removed according to the last-in first-out (LIFO)
  principle

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Stack ADT

• Methods
• push(o) insert object o at the top of the
  stack
• Input Object Output None
• pop() remove from the stack and return the
  top object on the stack an error occurs if
  the stack is empty
• Input None Output Object

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Stack ADT

• Methods
• size() return the number of objects in the
  stack
• Input None
• Output Integer
• isEmpty() return a Boolean indicating if the
  stack is empty or not
• Input None
• Output Boolean

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Stack ADT

• Methods
• top() return the top object on the stack,
  without removing it an error occurs if the
  stack is empty
• Input None
• Output Object

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Stack Illustration

• Create Stack of Characters

Output NONE
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Stack Illustration

• Push X

X
Output NONE
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Stack Illustration

• Push A

A
X
Output NONE
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Stack Illustration

• Push V

V
A
X
Output NONE
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Stack Illustration

• Size()

V
A
X
Output 3
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Stack Illustration

• Pop()

A
X
Output V
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Stack Illustration

• isEmpty()

A
X
Output FALSE
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Stack Illustration

• push V

V
A
X
Output NONE
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Stack Illustration

• top()

V
A
X
Output V
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Stack Implementation

• array-based Implementation
• has a fix size N
• has a pointer t that gives the index of the top
  element in the array S

S

0
1
t
2
N -1
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Stack Array Imp.

• Algorithm size()
• return t1
• Algorithm isEmpty
• return (tlt0)

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Stack Array Imp.

• Algorithm top()
• if isEmpty() then
• throw StackEmptyException
• return St

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Stack Array Imp.

• Algorithm push(o)
• if size() N then
• throw StackFullException
• t ? t 1
• St ? o

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Stack Array Imp.

• Algorithm pop()
• if isEmpty() then
• throw StackEmptyException
• e ? St
• t ? t 1
• return e

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Stack Array Imp.

• Running Time
• Method Time
• size O(1)
• isEmpty O(1)
• top O(1)
• push O(1)
• pop O(1)

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Example Stack of Char

• public class StackOfChar
• private int top-1
• private char S
• public StackOfChar()
• S new char5

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Example Stack of Char

• public int size()
• return top1
• public char top()
• return Stop

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Example Stack of Char

• public boolean isEmpty()
• return (toplt0)
• public void push(char c)
• Stop c

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Example Stack of Char

• public char pop()
• return Stop--
• // class StackOfChar

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Example Stack of Char

• public class main
• public static void main(String args)
• StackOfChar sc new StackOfChar()
• sc.push('A')
• System.out.println(sc.top())
• System.out.println(sc.isEmpty())