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Chapter 3

Chapter 3. Lists, Stacks, Queues. Abstract Data Types. A set of items Just items, not data types, nothing related to programming code A set of operations that can be performed on the items Nothing about HOW to do the operations For example add to the end Length of list.

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Chapter 3

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  1. Chapter 3 Lists, Stacks, Queues

  2. Abstract Data Types • A set of items • Just items, not data types, nothing related to programming code • A set of operations that can be performed on the items • Nothing about HOW to do the operations • For example add to the end • Length of list

  3. C++ Classes and ADT • The C++ class facility makes it easy to implement ADTs. • Hides the details from the user • Easy to change the details (would not have to change programs that use the class) • The interface (argument sequence) should never have to change (if it does, then it was a poor design).

  4. List (not linked list) • A basic ADT is a List. • A list holds a collection of items • Class roll • Shopping list • Each item has a position • Various operations • Print, makeEmpty, insert, remove, find • Must determine error conditions • Remove from empty list, find value not there…

  5. Implementations – Array • Very easy to use an array to implement the List ADT. • Fixed size • Easy to add and remove at the end • Easy to find • Very easy to find if list is ordered • Easy to go to a specified position (findKth) • “Hard” to add and remove from anywhere else • Must move items up or down (think of big lists) • NOTE: Easy and hard are computer time, not programmer effort.

  6. Implementation – Linked Lists • Easy to add to beginning • Can be easy to add to end (if keep an end pointer) • Easy to add after/before any position (just change pointers after you get to that position) • findKth not as easy as array based • Can be done with dynamic memory (no fixed size).

  7. Doubly Linked Lists • If we ever need to “back up” in a linked list, it will be very difficult. • Have to start at beginning, keep a previous pointer and go until get to “current” node. • Instead, have a node keep a previous (as well as next) link. • The first node’s previous will be NULL. • More pointers to change when inserting or deleting, but still just a fixed amount of code to execute – O(1). • Also makes insertInOrder easier (no need to keep a previous pointer.

  8. Stack • Last-in-First-out model. • The only real rule is that when we remove from a stack, we get the last thing added (that has not already been removed) • How that is implemented is up to the designer • Operations • Push, pop (mandatory) • Nice: top, size, isempty….

  9. Stack Implementation – Array • Keep an array and a variable to tell where the top of the stack is. • Push will put something into the array and change the top pointer • Pop will return a value and change the top pointer • Top will return a value and NOT change the top pointer

  10. Stack Implementation – Linked List • Use a linked list with just a few methods: • Push == insert at beginning • Pop == remove from beginning • Top == return value of first node

  11. Stack Uses • Find parentheses pairs (or any pairs {} []…) • Evaluating reverse polish (postfix) expressions • Infix to postfix conversion • Function call returns (allows recursion)

  12. Queues • Easy with Linked List (add to end, remove from the beginning). • Need to use a circular array when implementing with an array

  13. Header Node • Have a header node at the beginning of a linked list (node created in the constructor). • This way the Linked List always has a “NODE” (but it is not counted in the size). • Always skipped; has no data • Now, never have to check for empty list. • Never have to change the head pointer. • Most other methods have to be changed to account for the header node.

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