Arrays, Linked Lists, Stacks & Queues

Introduction

Efficiency is important

Focus on main memory data storage; data storage in secondary storage (e.g., hard disks and databases) is usually called indexing structures

Array

Array is a data structure that arranges items at equally spaced addresses in computer memory

int foo[7]

Unsorted Arrays

Pros:

• Array elements can be accessed by specifying the array name followed by the index in square brackets. Eg foo[2] is 8

• Efficient for insertion by appending a new element.

Cons:

• Have to scan through the whole array to determine for sure if an item is not there

Sorted Arrays

Pros:

• Efficient for searching

Cons:

• Have to move all items behind the point of insertion to make room for the new one

Linked Lists

A linked list is a data structure that allows both efficient searching and insertion/deletion.

A collection of items linked in a sequence:

Pros:

• Easy to insert/delete items in the middle, provided we know where to insert/delete (a sorted linked list can easily be maintained.)

Cons:

• Difficult to access the i-th item, given an arbitrary i

Stacks

A stack is a sequence of elements in which update can only happen at one end of the sequence, called the top.

Operations supported:

– push(x): add an element x to the top

– pop(x): remove the top element and return it in x, i.e., first-in-last-out (FILO)

Queues

CS3334 Lecture 3