Summary:
In this laboratory, we explore different issues related to searching.
Contents:
a. Start DrScheme.
b. If you have not done so already, please scan the
reading on searching.
In particular, you should look at the sample procedures.
Make sure that you understand the purpose of
get-key in binary-search.
c. Create a new file for this lab that contains the procedures
from that reading.
d. Create a vector, names, of a dozen or so lists, each of
which contains a last name and a first name. The first name and last
name should both be strings. Order the list by last name.
Include your name in the list. Include that vector in your file from
step c.
a. Using sequential-search-list, search for the letter
#\a in various lists of characters.
Note that it's probably easiest to create a list of characters
with string->list. For example,
> (string->list "hello")
(#\h #\e #\l #\l #\o)
Note also that you will need to create your own predicate for this
step of the exercise. I'd prefer that you'd create an anonymous
procedure (one in which you write the lambda without
a corresponding define).
b. Using sequential-search-vector, search for the letter
#\a in various vectors of characters.
c. Develop some tests for search-list-for-keyed-value.
For example, you might create a list of cartoon characters and their
sidekicks and search the list for character or sidekick. Here is
data for such a list.
| Protagonist |
Sidekick |
| Peabody |
Sherman |
| Yogi |
Booboo |
| Secret Squirrel |
Morocco Mole |
| Tennessee Tuxedo |
Chumley |
| Quick Draw McGraw |
Baba Looey |
| Dick Dastardly |
Muttley |
| Bullwinkle |
Rocky |
| Bart Simpson |
Milhouse Van Houten |
| Asterix |
Obelix |
| Fred |
Barney |
Write a procedure that takes a predicate and vector as parameters and,
using sequential-search-vector as a helper, finds a value
in the vector that matches the predicate or returns #f if no such value
exists. (Like sequential-search-vector, this procedure
searches vectors; unlike sequential-search-vector and like
sequential-search-list, this procedure returns a matching
value, rather than an index.
Add calls to display and newline to the
definition of binary-search, so that it prints out the values
of lower-bound and upper-bound each time the
kernel procedure is called. How many recursive calls are made as binary
search finds your name in the list names (from the
preparation)? How many are made in an unsuccessful search?
If you find you finish the lab early, please attempt one or more of
the following problems.
Define and test a Scheme procedure,
(search-file pred? port),
that reads in Scheme values from a given input
port, applying a specified test to each one. When it finds a value that
passes the test, it should return that value; if it gets the end-of-file
object before finding a value that passes the test, it should call the
error procedure to print an appropriate diagnostic.
The divide-and-conquer principle can be applied in other
situations. For example, we can apply it to a guessing game
in which one player, A, selects a number in the range from 1
to some value and the other player, B, tries to guess it by asking yes-or-no
questions of the form Is your number less than n?
(putting
in specific values for n). The most efficient strategy for B to
use is repeated bisection of the range within which A's number is known
to lie.
Write a Scheme procedure that takes the part of B in this game. Your
procedure should take the maximum possible value as a parameter. When
invoked, it should print out a question of the specified form and read in
the user's response (presumably, the symbol yes or the symbol
no), then repeat the process until the range of possible
values has been narrowed to contain only one number. The procedure should
then display and identify that number. A sample run might look like this:
> (guessing-game 100)
Is your number less than 51? yes
Is your number less than 26? no
Is your number less than 38? no
Is your number less than 44? no
Is your number less than 47? yes
Is your number less than 45? no
Is your number less than 46? no
Since your number is less than 47 but not less than 46, it must be 46.
;
Check with Bobby