Moooooo Or: How I learned to stop worrying and love USACO

Or: How I learned the solution to last week’s PotW 20 point solution: import java.io.*; public class PotW1 { public static void main(String[] Args) throws IOException { BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); int numCows = Integer.parseInt(in.readLine()); int ninjaCow = numCows; for (int i = 1; i < numCows; i++) ninjaCow = ninjaCow ^ i ^ Integer.parseInt( in.readLine()); System.out.println(ninjaCow); } }

General Info Main US high school programming contest o Sign up online - o Training pages - o Similar to USA(J)MO 6 contests each year Three divisions - Bronze, Silver, Gold o Silver and Gold are by invitation only o Higher divisions are more difficult Exact schedule TBD o Qualification round probably at end of October o The format for qualification round is different Again, TBD, so look for updates

Format problems hours (that's right: hours per problem!) Problems are algorithmic o Occasionally need some math Given a problem statement o And sample input / output o Write a program! o Subject to time and memory constraints o Multiple submissions allowed Last submission by end of contest will be tested o This test data is unknown to you o Get points for each test case you pass

Details Example: if the name of the task is "cowmilk" I/O o Scan from a file - "cowmilk.in" o Write to another file - "cowmilk.out" Header (place this comment at the top of code): /* ID: username TASK: cowmilk LANG: JAVA ( or C++ ) */ Read the rules for more details

Java I/O import java.io.*; import java.util.*; BufferedReader br = new BufferedReader(new FileReader("cowmilk.in")); Scanner s = new Scanner(new File("cowmilk.in")); PrintWriter o = new PrintWriter(new BufferedWriter(new FileWriter("cowmilk.out"))); In C++: #include using namespace std; fstream i("cowmilk.in"),o("cowmilk.out"); (yes, really)

Time Flies! Time limit is very important o Depends on the efficiency of your algorithm o e.g. how quickly can you add up the numbers from 1 - N? one step - N*(N+1)/2 o Java can do about 200,000,000 operations per second (grader scales to 700MHz) dividing doubles, calling methods, casting classes, etc. o Estimate how many operations your solution will do o C/C++ and Pascal are often faster than Java Memory is not that important Do not waste time making premature optimizations in speed o Often okay to sacrifice a little efficiency for ease of coding o Only make optimizations that can increase speed by an order of magnitude

STRATEGY Practice o Preferably before the contest Read each problem: o Read the problem again o Read the time / memory constraints o Read the sample input / output Think logically. Notice small details. Be flexible and creative. So you think you have a solution? o Make sure you can actually code your solution o Check if your solution works by hand before coding o Look for corner cases o Test your solution on your own data Feel free to skip problems - they are never in order of difficulty o Partial solutions are also good

PotW – The White Textfile In a fit of schizophrenic hatred for Microsoft, you decide to go "creep" around in Windows Explorer, normalizing all of your text files into a less "revolting" format. (sorry, no cows this time) Your goal is to take a text file, which is composed of words delimited by any whitespace (' ', '\n', '\t', '\r'), and convert it into a text file that is composed of words delimited by '\n' only. We will be using USACO conventions for I/O. Sample input ( "whitetext.in" ): " abcd dcba\nuvw\r\nz \t" Sample output ( "whitetext.out" ): "abcd\ndcba\nuvw\nz" - no ending or starting newlines (without the quotations, of course) You will receive 8 pts for each solution you submit (up to 16 total) The two solutions must be radically different.