Stacks

• There are several basic data structures that we need to discuss.
• The Stack is a very common tool in computer science.
  • It is a homogeneous collection of data.
  • It maintains the data by order inserted.
  • It is characterized by access
    • Last in first out (LIFO)
    • Or First in last out.
  • It has several basic operations
    • Push add an item to the stack
    • Pop remove the top item from the stack.
      • This should produce an error if the stack is empty.
      • In some implementations this also returns the top item.
    • Top return the top item on the stack without removing it.
      • This should produce an error if the stack is empty.
    • Size returns the number of items on the stack.
    • IsEmpty returns true if the stack is empty.
    • IsFull returns true if the stack is full
• Two common implementations for stacks
  • Array Based
    • In an array based implementation, the stack starts at position 0
    • There is an index, usually top
      • This points to the next available position in the stack.
      • It is normally initialized to be 0
      • As items are added it increases.
  • List Based
    • In a list based implementation, the top pointer is to the "head" of the list.
    • Items are added and removed at the top.
• A fairly simple stack problem is here.