CSC151 2007S, Class 43: Binary Search

Admin:
* Questions on HW14?
  * Can we use an anonymous procedure in defining tally-as?
    YES!
* EC for Kesho Scott lecture or Ferrett/Stewart
* EC for signing up for Psych Experiments conducted by your classmates.
* EC for participating in ONE pride week activity

Overview:
* About common algorithms.
* Searching.
* Binary search.
* Lab.

/Computer Science is the Study of Algorithms/

* Algorithm is a set of instructions for building a solution to a problem
* These past ten or so weeks:
  * Tools for expressing algorithms
  * Some problems in a variety of domains
* Computer scientists also try to identify common problems and
  then to write "the best possible" algorithm for solving those problems
* This week and next: Two common problems (and some famous solutions)
  * Searching - Given a collection of stuff, find something in the collection that meets particular criteria
    * Common type: Using "keyed values", find a value with a particular key
  * Sorting
    * Put things in order (typically using a key)

/Binary Search/

* Searching in a particular domain
  * Keyed values
  * Stored in an array
  * Ordered from smallest key to largest key
* Strategy:
  * Look in the middle of the remaining things
    * FOund it - Done
    * Middle is too small, throw away the left half
    * Middle is too large, throw away the right half

/Lab/

/Reflection/

* How do you know that the response from binary-search is correct?
  Hint: vector-ref
* Testing count-grades
  try using a grade of 11 (how many grades are less than 11)
  try using a grade of 256 (how many grades are less than 256)
 
* Emily's third-favorite part of 151 - The binary search demo