Data Structures Stacks

1
Data Structures - Stacks
2
What are data structures?

• Different ways to organize data
• What data structures have we used before?
• lists / arrays
• deck (Blackjack)
• and more!

3
Introducing the Stack

• LIFO Last In First Out
• How does a stack of trays/plates work?
• Start with an empty stack
• Place tray on top of stack
• Place another tray on top of the stack
• Remove tray on top from stack
• etc.
• PUSH data is pushed on TOP of the stack
• POP data is popped from TOP of the stack

4
Stack Example

• PUSH A
• PUSH C
• PUSH D
• PUSH C
• var1 POP
• var2 POP

5
Why do we use stacks?

• Used to keep track of things in the order that
  they occur
• Continually PUSH things onto the stack
• To go back, we POP things off the stack
• Example
• PUSH A
• PUSH C
• PUSH D
• PUSH C
• POP
• POP
• POP
• POP

6
Stack Implementation

• How do we implement a stack?
• class
• array or ArrayList
• Now lets see some code