computer science - advanced content uil computer science contest – advanced content mike scott...

Computer Science - Advanced Content

UIL Computer Science Contest – Advanced Content

Mike Scott

University of Texas at Austin


Agenda• A brief look at Computer Science• New topics for contest (Java 5.0)

– enhanced for loop– Regular Expressions– printf– Scanner class– Generic Collections– new general data structures– auto boxing and unboxing

• Doing programming problems


A Brief Look at Computer Science

• The UIL CS contest emphasizes programming

• Most introductory CS classes, both at the high school and college level, teach programming

• … and yet, computer science and computer programming are not the same thing!

• So what is Computer Science?


What is Computer Science?• Poorly named in the first place.

• It is not so much about the computer as it is about Computation.

• “Computer Science is more the study of managing and processing information than it is the study of computers.”

-Owen Astrachan, Duke University


So why Study Programming?

• Generally the first thing that is studied in Chemistry is stoichiometry.– Why? It is a skill necessary in order to study

more advanced topics in Chemistry

• The same is true of programming and computer science.


• “What is the linking thread which gathers these disparate branches into a single discipline? …it is the art of programming a computer. It is the art of designing efficient and elegant methods of getting a computer to solve problems, theoretical or practical, small or large, simple or complex.”

- C. A. R. Hoare• Sir Tony Hoare. Turing Award Winner.

Inventor of the quicksort algorithm


• “Programming is unquestionably the central topic of computing.

In addition to being important, programming is an enormously exciting intellectual activity. In its purest form, it is the systematic mastery of complexity. For some problems, the complexity is akin to that associated with designing a fine mechanical watch, i.e., discovering the best way to assemble a relatively small number of pieces into a harmonious and efficient mechanism. For other problems, the complexity is more akin to that associated with putting a man on the moon, i.e, managing a massive amount of detail.

In addition to being important and intellectually challenging, programming is a great deal of fun. Programmers get to build things and see them work.. What could be more satisfying? “

- John V. Guttag, Professor at MITresearch in AI, medical systems, wirelessnetworking


Outcomes of Computer Science


Computer Science Skills • Yes, the number of pure programming jobs has

declined• But, the total number of jobs in information technology

as surpassed the previous peak from 2000• “Even as computer science students are being

encouraged to take more courses outside their major, students in other disciplines are finding more often that they need to use, design and sometimes write computer programs.”

- Steve Lohr, NY Times, August 2005


New Topics for UIL

• Newest version of Java is 5.0

• A major release that added many new features, many of which make it easier to write programs

• more features = more flexibility = greater complexity


The enhanced for loop • a.k.a. the for-each loop• alternative for iterating through a set of valuesfor(Type loop-variable : set-expression) statement

• Set-expression is an array or a collection such as ArrayList– more generally, anything that implements the Iterable interface

• Type must be the data type of the elements of the array or collection

• logic error (not a syntax error) if try to modify an element in array via enhanced for loop


Enhanced for loop

public static int sumListEnhanced(int[] list){ int total = 0;

for(int val : list){ total += val;

System.out.println( val );}return total;

}

public static int sumListOld(int[] list){ int total = 0;

for(int i = 0; i < list.length; i++){ total += list[i];

System.out.println( list[i] );}return total;

}


Enhanced for loopint[] list = {1, 2, 3, 4};for( int val : list){ val = val + 2; // logic error System.out.println( val );}for(int val : list)

System.out.print( val );


Regular Expressions• “A regular expression (abbreviated as

regexp, regex or regxp) is a string that describes or matches a set of strings, according to certain syntax rules. Regular expressions are used by many text editors and utilities to search and manipulate bodies of text based on certain patterns. Many programming languages support regular expressions for string manipulation.”


Regular Expressions in Java

• In Java the Pattern class represents regular expressions

• Regular expressions are specified as Strings

• Regular expressions used for the split method in the String class to parse the String based on the regular expression


Syntax of Regular ExpressionsConstruct Matches

x The character x

. Any character

+, e.g. x+ One or more times, matches patterns of 1 or more x’s in a row

*, e.g. x* Zero or more times, matches patterns of 0 or more x’s in a row

[], e.g. [abc] Used to enclose character classes. Match one of the included characters or expressions. Matches any a, b, or c

-, e.g. [a-z] Used to specify a range, match any lower case letter

^, e.g. [^a] Negation. Everything but the specified expression. Matches everything besides lower case a. (^ by itself is start of line)

\d Predefined character class. (PCC) Any digit. Same as [0-9]

\D PCC. A non digit. Same as [^0-9]

\s PCC. A whitespace character: Same as [ \t\n\x0B\f\r]

\S PCC. A non whitespace character. Same as [^\s]


More Regular Expressions

• traditional split questions

• What if there were two spaces between each word and the regular expression was just “\s”?

Construct Matches

\w PCC. A word character. Same as [a-zA-Z_0-9]

\W PCC. A non word character. Same as [^\w]

String s = “Fair’s got nothing to do with it.”;String[] result = s.split( “\\s+” );// regular expression for 1 or more white space characters.// The split method breaks use the regular expression as// “delimiters”.for(String val : result)

System.out.println( val );


Another Regex Example

• Given the regular expression “a*b”

• What is the output of the following code?

String s = “Someabrandombtextabout nothing” +“aaaabdoes itaaamakeabSense?”;

String[] result = s.split( “a*b” );for(String val : result)

System.out.println( val );


Regular Expression Example

• Given a*b

• Where do matches occur in:

• “Someabrandombtextabout nothingaaaabdoes itaaamakeabSense?”


• 5 matches


Regular Expression Example• Order matters

• a*b is not the same as b*a

• Given b*a and the previous String



• 12 matches


printfFrom Cay Horstman’s homepage. “The march of progress.”1980: C

printf("%10.2f", x);1988: C++

cout << setw(10) << setprecision(2) << showpoint << x;1996: Java

java.text.NumberFormat formatter = java.text.NumberFormat.getNumberInstance();

formatter.setMinimumFractionDigits(2);formatter.setMaximumFractionDigits(2);String s = formatter.format(x);for (int i = s.length(); i < 10; i++)

System.out.print(' ');System.out.print(s);

2004: JavaSystem.out.printf("%10.2f", x);


printf details• public PrintStream printf(String format,

Object... args) • format - A format string as described in

Format string syntax. May contain fixed text and one or more embedded format specifiers

• args - Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The number of arguments is variable and may be zero.


printf details – Formatter class• The format specifiers for general, character, and numeric

types have the following syntax:

%[argument_index$][flags][width][.precision]conversion • The optional argument_index is a decimal integer indicating the position of the

argument in the argument list. The first argument is referenced by "1$", the second by "2$", etc.

• The optional flags is a set of characters that modify the output format. The set of valid flags depends on the conversion.

• The optional width is a non-negative decimal integer indicating the minimum number of characters to be written to the output.

• The optional precision is a non-negative decimal integer usually used to restrict the number of characters. The specific behavior depends on the conversion

• The required conversion is a character indicating how the argument should be formatted. The set of valid conversions for a given argument depends on the argument's data type.


Conversion Types for PrintfConversion Description

‘b’ or ‘B’ Result is a boolean

‘c’ or ‘C’ Result is a character

‘d’ Result is a decimal integer

‘o’ Result is an octal (base 8) integer

‘x’ or ‘X’ Result is a hexadecimal (base 16) integer

‘e’ or ‘E’ The result is a floating point number formatted as a decimal (base 10) number in computerized scientific notation

‘f’ The result is a floating point number formatted as a decimal (base 10) number.


printf Flags

Flag Description

- Result will be left justified

+ Result will always include a sign

‘ ‘ Result will include a leading space for positive values

‘0’ Result will be 0 padded

‘(‘ Result will enclose negative numbers in parenthesis


printf Examplesdouble d = 12.555;System.out.printf("%8.2f", d);System.out.printf(“%+8.2f”, d);System.out.printf(“%8.2d”, d);System.out.printf(“%-+8.2f”, (int)d);System.out.printf(“%+010.4f”, d);

double[] gpas; //code to initString[] names; //code to init

for(int i = 0; i < gpas.length; i++)System.out.printf(“Name: %-s GPA: %5.2f”,

names[i], gpas[i]);


Scanner class• A new class to allow simple parsing of input.

• Makes it easier to get input from System.in

• Methods for getting nextLine, nextInt, nextDouble, next String

• Set delimiters with regular expressions, default is whitespace

Scanner s = new Scanner(System.in); System.out.print("Enter your name: ");String name = s.nextLine();

System.out.print("Press Enter to continue: ");s.nextLine();


Hooking a Scanner up to a Fileimport java.util.Scanner;import java.io.File;import java.io.IOException;

public class ReadAndPrintScores{ public static void main(String[] args) { try

{ Scanner s = new Scanner( new File("scores.dat") ); while( s.hasNextInt() ) { System.out.println( s.nextInt() ); }}catch(IOException e){ System.out.println( e );}

}}

12 35 1212 45 12

12

13 57

scores.dat


Quick and Dirty Version

import java.util.*;import java.io.*

public class ReadAndPrintScores{ public static void main(String[] args) throws IOException { Scanner s = new Scanner( new File("scores.dat") );

while( s.hasNextInt() ){ System.out.println( s.nextInt() );}

}}


Generic Classes

• Java 5.0 introduces “generics”

• Previously genericity was achieved through inheritance and polymorphism– every object in Java was an Object

• Caused a lot of casting and uncertainty about whether data types were correct

• UIL will focus on generic collections


Generic ArrayList• old ArrayListArrayList list = new ArrayList();list.add(“UIL”);list.add(“CS”);String s = (String)list.get(0);

• new ArrayList

ArrayList<String> list = new ArrayList<String>();list.add(“UIL”);list.add(“CS”);String s = list.get(0);

• Old style still works– raw collections that generate compile time warnings


New Data Structures – Hash Table• Hash Table

– no Java class– HashSet and HashMap use Hash Tables as

the internal storage container to implement a Set and a Map

– Hash Tables rely on fast access into arrays if index is known

– Can achieve O(1) performance for add, access, and remove

– challenge is handling collisions


New Data Structures – Priority Queue

• Priority Queue– like a Queue, but every item added has a

priority– items get to move in front of other items in

already present in Queue that have a lower priority

– example: how patients are seen in an emergency room

– PriorityQueue class in the Java Standard Library


New Data Structures - Heap• A complete binary tree where every node has a

value more extreme (greater or less) than or equal to the value of its parent

• min and max heaps• example below is a min heap• min value at the root

5

12 7

32 45

37 55

13 9

50


Auto Boxing and Unboxing• In Java there is a big difference between the

primitive variables and objects• Collections could only contain objects• Adding primitives was a pain

ArrayList list = new ArrayList();for(int i = 0; i < 10; i++)

list.add( new Integer(i) );for(int i = 0; i < list.size(); i++)

System.out.println( ((Integer)list.get(i)).intValue() );

• Primitives have to be boxed or wrapped into objects


Auto boxing and unboxing• The system now automatically boxes and

unboxes primitives when adding to collections or other times an object is needed

ArrayList<Integer> list = new ArrayList<Integer>();for(int i = 0; i < 10; i++)

list.add( i );for(int i = 0; i < list.size(); i++)

System.out.println( list.get(i) + 2 );

// ORfor( int val : list )

System.out.println( val + 2 );


Programming Problems• Regional and State level only, for now…

• I am terrible artist– if I practiced I might get better

• Programming problems– the only way to get better is to pratice

• Sources of problems– UIL CS website. Old problems– online contests and judges


Keys to Success

• Reading from an input file– setting up a Scanner

• Hard problems -> Design first

• Test your solution against the sample data

• Realize judges data is different and may test boundary cases you didn’t consider


Example Problem 1Brain Plan

Program Name: brain.java Input File: brain.inResearchers are developing non-invasive devices that allow patients to control robotic arms using their minds. These devices examine the brainwave readings in patients to determine what action the robotic arm should take. Before the device can function, it needs to be programmed to associate certain brainwave patterns with robotic arm movements. To aid in this effort, two test subjects have had their brainwave readings taken when trying to get the robotic arm to perform specific actions.

Your job is to generalize the sets of brainwave readings into brainwave patterns that the device can use for comparisons in upcoming trials. Brainwave scans from the test subjects show only active and inactive portions of the brain. From these scans, a pattern can be deduced by determining where the scans agree and where they disagree. Areas of agreement indicate portions of the pattern that should be active (or inactive) while disagreements indicate portions of the pattern that should be marked as unimportant.


Example Problem 1Brainwave scans are strings of 18 characters where each character represents a portion of the brain that is either 'A'=Active or 'I'=Inactive. Patterns are also strings of 18 characters where 'A'=Active, 'I'=Inactive, and '*'=Unimportant.

For instance, the following pair of brainwave scans:AAAAIIIIIIIIIAAIAIIIAAIIIIAIIIIAIIAI

gives rise to the pattern:

**AAIIII*IIIIA*IAI


Example Problem 1InputThe first line will contain a single integer n indicating the number brainwave scans pairs that need to have their patterns calculated. Each pair of the next 2n lines will contain brainwave scans for different actions.

OutputFor each brainwave scan pair in the input, output the corresponding brainwave pattern on its own line. Example Input File 3

AAAAIIIIIIIIIAAIAIIIAAIIIIAIIIIAIIAIAAAAAAAAAIIIIIIIIIIIIIIIIIIAAAAAAAAAAIAIAIAIAAIAIAIAIAIAIAIAIAIAIAAAIAAI

Example Output To Screen**AAIIII*IIIIA*IAI***************************AIA*AIA**


Brain Problem Design• Hook up Scanner to file.

– No path info!

• Read line for number of data sets• For each data set

– read in line 1– read in line 2– iterate through each line and compare to create result

• print out result• a relatively easy problem


Example Problem 2Juggling NumbersProgram Name: juggle.java Input File: juggle.inDid you ever wonder how jugglers can keep track of all of those balls while not letting any of them fall? They do it by mastering a certain number of basic throws and then chaining them together in exciting ways.One convenient side-effect of this technique is that it is possible to represent a jugging pattern fairly well with a string of single digits such as “5313” or “441441”. Each digit represents a single throw, with the height of the throw corresponding to the size of the number (the exception is the 0 digit, which represents no ball is thrown during that step). For instance, a ball thrown with a height of 5 will have to be caught five steps later in the sequence. Not all sequences are possible for jugglers, however, since they can only catch one ball during any given step. In the sequence “321” all three balls would be landing during step 4! It’s very useful to be able to determine whether or not a sequence is possible.


InputThe first line of input will contain a single integer n indicating the number of datasets.The following n lines will each contain a sequence of digits (0-9) representing a juggling pattern. Each sequence will contain from 1 to 40 digits.OutputFor each dataset in the input, determine if there is any step where more than one ball must be caught. If there is no such step, then the sequence is valid and the string “VALID” should be displayed. Otherwise, for sequences with steps where multiple balls have to be caught simultaneously, the sequence is invalid, and we want to know the number of balls that will drop the first time the juggler misses. This value should be one less than the total number of balls that need to be caught during the first step where the juggler has to catch more than one. In the case of an invalid sequence, display “DROPPED X on step Y”, where the first drop occurs on step Y, with X balls missed, and steps are numbered starting at 1.Note the sequences will likely end with some balls still in the air. Solutions should treat this situation as if the sequence ended in just enough zeros (“0”) to ensure all balls were caught.


Example Input File4333333333441441441441333321445441441441Example Output To ScreenVALIDVALIDDROPPED 2 on step 7DROPPED 1 on step 8


Judges data file for Juggle

1033333333344144144144133332144544144144150990012345678998765432100009070301

Expected Output

VALIDVALIDDROPPED 2 on step 7DROPPED 1 on step 8VALIDVALIDVALIDVALIDDROPPED 8 on step 10DROPPED 1 on step 11

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