UIL Computer Science
Contest – Advanced Content
Mike Scott
University of Texas at Austin
Computer Science - Advanced Content
Agenda
• A brief look at Computer Science
• New topics for contest (Java 5.0)
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enhanced for loop
Regular Expressions
printf
Scanner class
Generic Collections
new general data structures
auto boxing and unboxing
• Doing programming problems
Computer Science - Advanced Content
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?
Computer Science - Advanced Content
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
Computer Science - Advanced Content
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.
Computer Science - Advanced Content
• “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
Computer Science - Advanced Content
• “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 MIT
research in AI, medical systems, wireless
networking
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Outcomes of Computer Science
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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
Computer Science - Advanced Content
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
Computer Science - Advanced Content
The enhanced for loop
• a.k.a. the for-each loop
• alternative for iterating through a set of values
for(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
Computer Science - Advanced Content
Enhanced for loop
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;
}
public static int sumListEnhanced(int[] list)
{
int total = 0;
for(int val : list)
{
total += val;
System.out.println( val );
}
return total;
}
Computer Science - Advanced Content
Enhanced for loop
int[] 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 );
Computer Science - Advanced Content
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.”
Computer Science - Advanced Content
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
Computer Science - Advanced Content
Syntax of Regular Expressions
Construct
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]
Computer Science - Advanced Content
More Regular Expressions
Construct
Matches
\w
PCC. A word character. Same as [a-zA-Z_0-9]
\W
PCC. A non word character. Same as [^\w]
• traditional split questions
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 );
• What if there were two spaces between each word and
the regular expression was just “\s”?
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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 );
Computer Science - Advanced Content
Regular Expression Example
• Given a*b
• Where do matches occur in:
• “Someabrandombtextabout
nothingaaaabdoes itaaamakeabSense?”
• “Someabrandombtextabout
nothingaaaabdoes itaaamakeabSense?”
• 5 matches
Computer Science - Advanced Content
Regular Expression Example
•
•
•
•
Order matters
a*b is not the same as b*a
Given b*a and the previous String
“Someabrandombtextabout
nothingaaaabdoes itaaamakeabSense?”
• “Someabrandombtextabout
nothingaaaabdoes itaaamakeabSense?”
• 12 matches
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printf
From 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: Java
System.out.printf("%10.2f", x);
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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.
Computer Science - Advanced Content
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.
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Conversion Types for Printf
Conversion
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.
Computer Science - Advanced Content
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
Computer Science - Advanced Content
printf Examples
double 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 init
String[] names; //code to init
for(int i = 0; i < gpas.length; i++)
System.out.printf(“Name: %-s GPA: %5.2f”,
names[i], gpas[i]);
Computer Science - Advanced Content
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();
Computer Science - Advanced Content
Hooking a Scanner up to a File
import 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() );
12 35 12
}
12 45
}
12
catch(IOException e)
{
System.out.println( e );
12
}
}
}
13 57
scores.dat
Computer Science - Advanced Content
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() );
}
}
}
Computer Science - Advanced Content
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
Computer Science - Advanced Content
Generic ArrayList
• old ArrayList
ArrayList 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
Computer Science - Advanced Content
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
Computer Science - Advanced Content
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
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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
32
37
7
45
55
13
50
Computer Science - Advanced Content
9
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
Computer Science - Advanced Content
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 );
// OR
for( int val : list )
System.out.println( val + 2 );
Computer Science - Advanced Content
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
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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
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Example Problem 1
Brain Plan
Program Name: brain.java
Input File: brain.in
Researchers 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.
Computer Science - Advanced Content
Example Problem 1
Brainwave 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:
AAAAIIIIIIIIIAAIAI
IIAAIIIIAIIIIAIIAI
gives rise to the pattern:
**AAIIII*IIIIA*IAI
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Example Problem 1
Input
The 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.
Output
For each brainwave scan pair in the input, output the corresponding
brainwave pattern on its own line.
Example Input File
3
AAAAIIIIIIIIIAAIAI
IIAAIIIIAIIIIAIIAI
AAAAAAAAAIIIIIIIII
IIIIIIIIIAAAAAAAAA
AIAIAIAIAAIAIAIAIA
IAIAIAIAIAIAAAIAAI
Example Output To Screen
**AAIIII*IIIIA*IAI
******************
*********AIA*AIA**
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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
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Example Problem 2
Juggling Numbers
Program Name: juggle.java
Input File: juggle.in
Did 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.
Computer Science - Advanced Content
Input
The 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.
Output
For 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.
Computer Science - Advanced Content
Example Input File
4
333333333
441441441441
333321
445441441441
Example Output To Screen
VALID
VALID
DROPPED 2 on step 7
DROPPED 1 on step 8
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Judges data file for Juggle
Expected Output
10
333333333
441441441441
333321
445441441441
5
09
90
0123456789
9876543210
0009070301
VALID
VALID
DROPPED 2 on step 7
DROPPED 1 on step 8
VALID
VALID
VALID
VALID
DROPPED 8 on step 10
DROPPED 1 on step 11
Computer Science - Advanced Content