Section: Pset5Jordan Jozwiak

CS50

AnnouncementsPset4 will be returned by Tuesday night (but

hopefully tonight!)If you haven’t already, pick up Quiz 0 at end

of class!Don’t forget to add music to our

coding playlist!Link sent out via email last week

This WeekBrief Feedback/Questions for Pset4Section of Questions (and brief discussion

with slides)Stack (~10 min)Queue (~10 min)Singly Linked lists (~50 min)

If time…Hash tables

Pset4 Feedbackbf.bfSize vs. bi.biSizeImage

bf.bfOffBitsuint8_t, uint32_t, int32_t, and uint16_tJunk data in an image – image appears the

same but it has a larger file size? How?

Does your TF try too hard?Forensics 2011 Forensics 2012

Stacks

Last in, first out data structure.

Can ‘pop’ or ‘push’ things to the top of the stack.

Top

Queues

First in, first out data structure.

“Insert” and “Remove” operations.

Head Tail

Linked ListsData structure composed of a set of structs.Each struct contains a piece of data and a

pointer to the next struct.

42 50typedef struct node { int num; struct node *next;} node;

struct node

null

int numstruct node

*next

Linked ListsUnlike an array, linked lists allow us to insert

or remove elements in constant time!

42

35

50 NULL

Hash TablesConsists of an array and a hash function.Hash function maps input to an index in the

associated array.Allows us to check whether something is

contained in a data structure without checking through the entire thing.

Hash TablesGood Hash Functions are:DeterministicUniformly distributed

intxkcd_hash(char *word){ return 4;}

THIS IS

BAD

Hash Tables: with Linked Lists

Coding time!!!stack.c (~10 min)queue.c (~10 min)sll.c (~50 min)

Get the code…cd ~/Dropboxwget http://

cdn.cs50.net/2012/fall/sections/6/section6.zipunzip section6.zip

On your way out…Don’t forget about the BIG BOARD! (give it a

shot)Remember that you can access section

powerpoints and SOQ solutions at http://cloud.cs50.net/~jjozwiak/