Current Hiring Puzzles

The BitVectors are an ancient and immortal race of 10,000, each with a 10,000 bit genome. The race evolved from a single individual by the following process: 9,999 times a BitVector chosen at random from amongst the population was cloned using an error-prone process that considers each bit independently, and flips it with 20% probability.

Write a program to guess the reproductive history of BitVectors from their genetic material. The randomly-ordered file bitvectors-genes.data.gz contains a 10,000 bit line for each individual. Your program's output should be, for each input line, the 0-based line number of that individual's parent, or -1 if it is the progenitor. Balance performance against probability of mistakes as you see fit.

To help you test your program, here is a much smaller 500 x 500 input dataset:bitvectors-genes.data.small.gz, along with its solution file: bitvectors-parents.data.small.
 

Write a Java web application which provides "instant search" over properties listed in the National Register of Historic Places. Rather than waiting for the user to press a submit button, your application will dynamically update search results as input is typed. We provide the file nrhp.xml.gz, which contains selected information from the register's database.

Database The key component of your server-side application is an efficient, in-memory data structure for looking up properties (written in pure Java). A good solution may take several minutes to load, but can answer a query in well under 0.1 ms on a modern PC. (Note that a sequential search of all properties is probably too slow!) An input matches a property if it is found at any position within that property's names, address, or city+state. Matches are case-insensitive, and consider only the characters A-Z and 0-9, e.g. the input "mainst" matches "200 S Main St" and "red" matches "Lakeshore Dr." Note that the server's JVM will be configured with 1024M maximum heap space. Please conform to the interfaces specified in nrhp.jar when creating your database.

Servlet Your servlet should accept an input string as the request parameter to a GET request. Results should include the information for a pre-configured number of properties (e.g. 10), the total number of matches which exist in the database, and the time taken by your search algorithm. Your servlet should be stateless, ie. not depend on any per-user session information. Paginate your additional results as a bonus!

Client Your web page should access the servlet using JavaScript's XMLHttpRequest object. As the user types, your interface should repeatedly refine the list of search results without refreshing the page.

Please submit a WAR file, configuration instructions, your source code, and any comments on your approach. Your application will be tested with Tomcat on Sun's 64-bit J2SE and a recent version of Firefox.
 

Resources XMLHttpRequest, StAX, Apache Tomcat, Mozilla Firefox, Eclipse
 

 

Implement a simple standalone TCP-based chat server, using the following protocol:

The server responds to all commands with either:

						OK<CRLF>

or, when an error occurred, with:

						ERROR <reason><CRLF> 

<CRLF> indicates the bytes '\r\n'.

Upon connecting to the server, the client sends:

						LOGIN <username><CRLF> 

Clients can create new chatrooms or join existing chatrooms (chatrooms begin with the character '#') by doing:

						JOIN #<chatroom><CRLF>

Clients can leave chatrooms by sending:

						PART #<chatroom><CRLF>

Clients can be in multiple chatrooms at once.

Clients can send a message to a chatroom:

						MSG #<chatroom> <message-text><CRLF> 

Clients can send a message to another user:

						MSG <username> <message-text><CRLF>  

When a message is sent to a chatroom the user is in, the server sends to the appropriate client:

						GOTROOMMSG  <sender> #<chatroom> <message-text><CRLF> 

or if the message is sent directly from one user to another:

						GOTUSERMSG <sender> <message-text><CRLF>  

Finally, the client can log off by sending:

						LOGOUT<CRLF>

Here's a transcript of a sample session where a user named "alice" joins a chatroom called #news after connecting. C indicates the line was sent by the client, S indicates it was sent by the server (end of line indicates CRLF was sent):

C: LOGIN alice

S: OK

C: JOIN #news

S: OK

C: MSG #news hi everyone

S: GOTROOMMSG bob #news nothing much happened after that

S: OK

S: GOTROOMMSG alice #news hi everyone

S: GOTUSERMSG carol hi alice, where've you been?

C: MSG carol on vacation

S: OK

C: LOGOUT



When implementing the server, aim for scalability and robustness. (Many submissions fail due to lack of robustness!) Your submission should include a description of the steps you took towards those two goals. Keep in mind that the client may be buggy, or even malicious. For example, if a client connects to the server and sends an infinite stream of the byte 'X' with no line break, the server should deal with this case gracefully. Please do not use an existing networking framework (e.g., Twisted or asyncore for Python, ACE for C++, etc.) to implement the server. The server should support running on Linux. 
 

Objective You want to meet a friend at O'Hare airport at noon and return home the same day. Given a date and an origin airport, find the pair of nonstop flights that gets you to Chicago and home again on that date, minimizing your total time away from home, subject to the constraint that you are at O'Hare at noon. 

Details Your program, which must be written in Java, will work by scraping our http://matrix2.itasoftware.com website. Your program should accept two command-line inputs as follows: 

java -jar OHareAffair.jar YYYY-MM-DD airportCode

The program should navigate to matrix2.itasoftware.com and pose a round-trip query between the given airportCode and O'Hare (ORD), limited to nonstop flights only, using BOS as the sales city, with appropriate date and time constraints. The program should then scan the resulting solution set for solutions that meet the objective specified above. No more than 15 http requests should be made of matrix2.itasoftware.com per invocation. Finally, details of the three shortest solutions (breaking ties arbitrarily) should be written out in human-readable form to the console.

For example, for a traveler from Baltimore on July 4th, your program might be invoked as follows: 

java -jar OHareAffair.jar 2006-07-04 BWI

Sample output:

Travelling round-trip from BWI to ORD on 2006-07-04:
Trip length: 6:21
Outbound: American Airlines Flight AA3991 (10:03a-11:04a)
Return: United Airlines Flight UA1236 (1:30p-4:24p)
Trip length: 6:39
Outbound: United Airlines Flight UA641 (9:45a-10:47a)
Return: United Airlines Flight UA1236 (1:30p-4:24p)
Trip length: 6:54
Outbound: American Airlines Flight AA3991 (10:03a-11:04a)
Return: American Airlines Flight AA4009 (2:09p-4:57p)

Strive to make your code clean and robust, and to report errors cleanly. Be sure to include your source, any necessary libraries, and instructions on how to run it. 
 

Strawberries are growing in a rectangular field of length and width at most 50. You want to build greenhouses to enclose the strawberries. Greenhouses are rectangular, axis-aligned with the field (i.e., not diagonal), and may not overlap. The cost of each greenhouse is $10 plus $1 per unit of area covered.

Write a program that chooses the best number of greenhouses to build, and their locations, so as to enclose all the strawberries as cheaply as possible. Heuristic solutions that may not always produce the lowest possible cost will be accepted: seek a reasonable tradeoff of efficiency and optimality.

Your program must read a small integer 1 ≤ N ≤ 10 representing the maximum number of greenhouses to consider, and a matrix representation of the field, in which the '@' symbol represents a strawberry. Output must be a copy of the original matrix with letters used to represent greenhouses, preceded by the covering's cost. Here is an example input-output pair:

Input		Output
4 ..@@@@@............... ..@@@@@@........@@@... .....@@@@@......@@@... .......@@@@@@@@@@@@... .........@@@@@........ .........@@@@@........		90 ..AAAAAAAA............ ..AAAAAAAA....CCCCC... ..AAAAAAAA....CCCCC... .......BBBBBBBCCCCC... .......BBBBBBB........ .......BBBBBBB........

In this example, the solution cost of $90 is computed as (10+8*3) + (10+7*3) + (10+5*3).

 

Run your program on the 9 sample inputs found in this file and report the total cost of the 9 solutions found by your program, as well as each individual solution.