CS 261 Fall 2006

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CS 261 - Fall 2006

• Linked List Introduction

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Characteristics of Linked Lists

• Elements are held in objects termed Links
• Links are 1-1 with elements, allocated and
  released as necessary.
• Each link points to next link in sequence,
  sometimes to previous link.
• Lots of variations on a simple idea

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A typical Link Structure

• struct slink / single link /
• EleType value
• struct slink next

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Some variations in Linked lists

• List have header (special value to point to
  start)
• Use null as terminator, or special value for end
• Use single or double links?
• Pointer to first element, or pointer to first and
  last

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Simplest Example, List Stack

• List stack is the simplest data structure that
  can be implemented using linked list idea
• Keep pointer to first element (null if empty)
• Elements are added or removed from front
• can only access first element

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Picture of list stack
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Code for list stack

• struct ListStack
• struct slink firstLink / initialize
  routine sets to zero /
• void listStackPush (struct listStack stk, double
  val)
• / you are going to write this /
• Malloc a new link (check that it works!)
• Set data fields in the new link
• Change firstLink to point to new link

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What about other operations?

• How do you tell if the stack is empty?
• How do you return the first element?
• How do you remove an element?

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How fast is List Stack?

• Compare to dynamic array Stack
• push - list O(1) always, dyArray(1) expected
• pop - list O(1) always, dyArray same
• top - list O(1) always, dyArray same
• In practice dyArray is slightly faster in real
  timings.

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Your turn

• Complete the worksheet on the linked list stack
• Tomarrow - New topic - Queues
• Read the chapter posted on web site.