Feb 1

discuss homework

How far did you get?

more C

multiple files :

.h files
make and Makefilefd

pointers :

 char* name = "Jim Mahoney";
 int* list1;  // all three essentially same
 int *list2;  //
 int list3[]; //

Note that none of those three actually creates space for an array; they all set up a place for a pointer to an integer. Which can be also be a pointer to the first of many integers, i.e. an array.

 int x = 3;
 int* x_ptr = &x;
 *x_ptr = 7;   // the value of x is now changed.
 
 int foo[3] = {10, 11, 12};  // curlies only during initialization
 foo[1] = 21;                // modify middle entry
 *(foo +2) = 7;              // same(!!) : "dereference 2 integers past foo"

I attached the play.c that we did in class.

work through my C code

Discuss mercurial, and code repositories briefly.

discuss quicksort, radix sort

quicksort:

The central idea is a "pivot": sort numbers below, numbers above into two sublists. And can be done in place!
wikipedia: quicksort

radix sort:

If you have unique integers and enough space to number 'em all, you can just plop 'em in place.
Or, you can sort into bins digit by digit in (say) base 10, so that up to 1000 can be done in 4 passes. But
So is it linear time? Hmmm.
wikipedia: radix sort

Both of these are average O(n log(n)); both are good depending on situation. And both are "divide and conquer" algorithms.

fourier

Review: complex numbers, complex exponentials, vectors, dot products, and finding components.

Discuss continuous vs discrete representations of functions f(time) and F(freq). Start building some intuition for the big ideas.

(Probably on Thu) work out the fourier transfer relations.

http://cs.marlboro.edu/ courses/ spring2011/algorithms/ notes/ Feb_1
last modified Tuesday February 1 2011 3:26 pm EST

attachments

name last modified size

Algorithms

course