Programming%20Interest%20Group

1
Programming Interest Group

• Tutorial One
• Introduction
• Get Familiar with Your Weapon

2
What is ACM?

• ACM Association for Computing Machinery
• http//www.acm.org/
• the worlds largest educational and scientific
  computing society
• ACM ICPC
• ACM International Collegiate Programming Contest
• http//en.wikipedia.org/wiki/ACM_International_Col
  legiate_Programming_Contest

3
ACM ICPC

• ICPC is a two-tiered competition among teams of
  students representing institutions of higher
  education.
• Teams compete in Regional Contests, from which
  top scoring teams advance to the ACM-ICPC World
  Finals.
• Each team has three students, sharing one
  computer, given a number of programming problems
• Coordination and teamwork are essential

4
Online Judge (OJ)

• When you finish a problem, submit the source code
  to the online judge
• You can use C, C, Java
• The online judge will compile your source code,
  and check with unknown number of secret test
  cases
• Feedback from the judge
• Accepted (AC) congratulations!
• Presentation Error (PE) Your program outputs
  are correct, but are not presented in the
  specified format. Check for spaces, left/right
  justification, line feeds, etc.
• Wrong Answer (WA) Your program returned an
  incorrect answer to one or more of the judges
  secret test cases
• Compile Error (CE) The judges compiler cannot
  compile your source code

5
Online Judge (cont.)

• Runtime Error (RE) Your program failed during
  execution due to a segmentation fault, floating
  point exception, or others.
• Time Limit Exceeded (TL) Your program took too
  much time on at least one of the test cases. Try
  to improve the efficiency of your solution!
• Memory Limit Exceeded (ML) Your program tried
  to use more memory than the judges settings.

6
Available OJs

• There are many famous online judges
• Valladolid OJ (http//acm.uva.es/p)
• Ural OJ (http//acm.timus.ru)
• Saratov OJ (http//acm.sgu.ru)
• ZJU OJ (http//acm.zju.edu.cn)
• ZJUT OJ (http//acm.zjut.edu.cn)
• Official ACM Live Archive (http//cii-judge.baylor
  .edu/)
• Peking University Online Judge (http//acm.pku.edu
  .cn/JudgeOnline/)
• Programming Challenges (http//www.programming-cha
  llenges.com)

7
What do we use?

• Programming Challenges
• Steven S. Skiena and Miguel Revilla, Programming
  Challenges, the Programming Contest Training
  Manual, Springer, 2003.
• http//www.programming-challenges.com/pg.php?page
  index
• Our main training reference, available from
  library

8
Suggested Books

• Art of Programming Contest (free online)
• http//online-judge.uva.es/p/Art_of_Programming_Co
  ntest_SE_for_uva.pdf
• Thomas H. Cormen, Charles E. Leiserson, Ronald L.
  Rivest, and Clifford Stein, Introduction to
  Algorithms, 2nd Edition, The MIT Press, 2001.
• Robert Sedgewick, Bundle of Algorithms in Java,
  Third Edition (Parts 1-5), 3rd Edition,
  Addison-Wesley Professional, 2003. (There is also
  a C version).
• Donald E. Knuth,The Art of Computer Programming,
  Volume 1, 2, 3.
• Bill Gates said that in order to be "a really
  good programmer" one must read its first volume
  and solve all of its problems before sending his
  company a resume.

9
Programming Languages

• Machine Language
• Or called Machine code, understandable directly
  by CPU
• Different CPU has different Instruction Set
• A program is just a sequence of instructions that
  are executed by a CPU.
• E.g. adding registers 1 and 2 and placing the
  result in register 6 is encoded as
• 000000 00001 00010 00110 00000 100000

10
Machine Language

• Shall we understand the so cold binary code?
• CPU designer
• Writing an assembler
• Reverse-engineering
• http//www.reverse-engineering.net/
• A book
• Hacker Disassembling Uncovered by Kris Kaspersky

11
Assembly Language

• The same as machine language. But the command
  numbers are replaced by letter sequences,
  understandable by CS students.
• Assembler transform the assembly language into
  machine code
• E.g.

movl 1, eax movl 0, ebx int 0x80
12
Assembly Language

• Shall we learn assembly language today?
• Write an Operating System
• Write a compiler
• Optimize the performance of a piece of program
• MMX, SSE, SSE2, etc.
• Help us to understand how computer works!
• A free book Programming from the Ground Up, by
  Jonathan Bartlett

13
High-level Language

• Allow us to describe the program in a more
  natural language.
• A comparison of different programming languages
• http//en.wikipedia.org/wiki/Comparison_of_program
  ming_languages
• Compilation vs. Interpretation
• Interpreters are generally slower to run, but
  more flexible than compilers.

14
C

• Quoted from wikipedia
• The C programming language (often, just "C") is a
  general-purpose, procedural, imperative computer
  programming language developed in the early 1970s
  by Dennis Ritchie for use on the Unix operating
  system.
• KR C
• In 1978, Dennis Ritchie and Brian Kernighan
  published the first edition of The C Programming
  Language. This book, known to C programmers as
  "KR," served for many years as an informal
  specification of the language. The version of C
  that it describes is commonly referred to as "KR
  C."

15
C

• ANSI C and ISO C
• The first standard for C was published by ANSI.
• After a long and arduous process, the standard
  was completed in 1989 and ratified as ANSI
  X3.159-1989 "Programming Language C." This
  version of the language is often referred to as
  ANSI C, or sometimes C89.
• In 1990, the ANSI C standard (with a few minor
  modifications) was adopted by the International
  Organization for Standardization (ISO) as ISO/IEC
  98991990. This version is sometimes called C90.
  Therefore, the terms "C89" and "C90" refer to
  essentially the same language.
• ANSI C is now supported by almost all the widely
  used compilers.

16
C

• C99
• After the ANSI standardization process, the C
  language specification remained relatively static
  for some time, whereas C continued to evolve.
• A new C standard is finally published as ISO
  98991999 in 1999. This standard is commonly
  referred to as "C99." It was adopted as an ANSI
  standard in March 2000.
• Some new features
• Inline functions
• Variables can be declared anywhere
• Variable-length arrays
• Support for one-line comments beginning with //

17
C Books

• C Programming Language, 2nd Edition, by Brian W.
  Kernighan and Dennis M. Ritchie.
• Expert C Programming deep C secrets, by Peter
  van der Linden.
• The Standard C Library, by P. J. Plauger.

18
C

• Stroustrup began work on C with Classes in 1979.
• In 1983, the name of the language was changed
  from C with Classes to C.
• In 1985, the first edition of The C Programming
  Language was released.
• As the C language evolved, a standard library
  also evolved with it, which finally leaded to
  Standard Template Library (STL).
• After years of work, a joint ANSI-ISO committee
  standardized C in 1998 (ISO/IEC 148821998).
• The 1998 C standard consists of two parts the
  core language and the C standard library the
  latter includes most of the Standard Template
  Library and a slightly modified version of the C
  standard library.
• A newer version of C standard was published in
  2003.

19
C

• C can be thought of as comprising three parts
• The low-level language, largely from C
• Object-Oriented programming to define our own
  data types and to organize large-scale programs
  and systems
• Standard library to provide a set of useful data
  structures and algorithms

20
C

• Templates and Generic programming
• Generic programming involves writing code in a
  way that is independent of any particular type.
• Templates are the foundation of generic
  programming.

int compare(const string v1, const string
v2) if (v1 lt v2) return -1 if(v2 lt
v1) return 1 return 0
int compare(const double v1, const double
v2) if (v1 lt v2) return -1 if(v2 lt
v1) return 1 return 0
21
C

• The following is a template version of compare

Template lttypename Tgt int compare(const T v1,
const T v2) if (v1 lt v2) return -1
if(v2 lt v1) return 1 return 0
22
C Books

• C Primer
• C Primer Plus
• Thinking in C
• The C Programming Language, by Bjarne
  Stroustrup
• The C Standard Library A Tutorial and
  Reference , by Nicolai M. Josuttis

23
Java

• Java was started as a project called "Oak" by
  James Gosling in June 1991.
• The first public implementation was Java 1.0 in
  1995. It made the promise of "Write Once, Run
  Anywhere" (WORA), with free runtimes on popular
  platforms.
• Java remains a proprietary de facto standard that
  is controlled through the Java Community Process
  (http//www.jcp.org/en/home/index).

24
Java

• Object-Oriented programming
• Platform independence
• It means that programs written in the Java
  language must run similarly on diverse hardware.
  One should be able to write a program once and
  run it anywhere.
• Java language code ? Java bytecode
• Jave bytecode is then run on a virtual machine
  (VM), a program written in native code on the
  host hardware that interprets and executes
  generic Java bytecode.
• To improve the performance, Just-in-time (JIT)
  compilation has been introduced, by translating
  bytecode into native machine code at runtime.

25
Java Libraries

• Core libraries
• Data structures
• XML parsing libraries
• Security
• Internationalization and localization
• Integration libraries
• The Java Database Connectivity (JDBC) API for
  database access
• Java Naming and Directory Interface (JNDI) for
  lookup and discovery
• RMI and CORBA for distributed application
  development
• User interface libraries
• AWT (Abstract Windowing Toolkit )
• Swing
• APIs for audio capture, processing, and playback
• Lots of extensions
• Java EE (J2EE), Java ME (J2ME)
• JMF (Java Media Framework)
• JAI (Java Advanced Imaging)
• Java 3D, JOGL (Java OpenGL)

26
Others

• Python
• Rumor advocated by Google
• "Python has been an important part of Google
  since the beginning, and remains so as the system
  grows and evolved. Today dozens of Google
  engineers use Python, and we're looking for more
  people with skills in this language"-- Peter
  Norvig, Director of Search Quality at Google
• I am the author of the Python programming
  language. In December 2005 I joined Google in
  Mountain View, CA.-- Guido van Rossum, Creator
  of Python
• C
• Developed by Microsoft (to combat Java)

27
Standard Input/Output

• In ACM contest, each program must read the test
  data from the standard input and print the
  results to the standard output
• For C language, use scanf() and printf()
• For C, use cin and cout
• scanf() and printf() are also supported
• For Java, refer to http//www.programming-challeng
  es.com/pg.php?pagejavainfo
• Programs are not allowed to open files or to
  execute certain system calls

28
Not convenient for debugging?

• include ltstdio.hgt
• int main ()
• freopen(FILE_NAME_FOR_INPUT,r,stdin)
• freopen(FILE_NAME_FOR OUTPUT,w,stdout)
• Rest of the codes
• return 0

While sending your code to online judges,
remember to remove the two lines with freopen.
29
Simple Coding

• Avoid the usage of the or -- operators inside
  expressions or function calls
• Avoid expressions of the form p
• Avoid pointer arithmetic. Instead of (p5) use
  p5.
• Never code like return (xy)Func(t)/(1-s)
• but like
• temp func(t)
• RetVal (xy) temp/(1-s)
• return RetVal

30
Naming

• Dont use small and similar names for your
  variables. Use descriptive names.
• Dont use names like i,j,k for loop control
  variables. Use I,K,M.
• It is very easy to mistake a j for an i when you
  read code or copy, paste change code,

31
Internal force

• Data Structures
• Commonly seen in almost every programming
  projects
• A treasure from tens of years of experiences
• Summarized by computer scientists as textbooks
• A core subject for every computer
  science/computer engineering department

32
Internal force

• Algorithms
• To solve real problems efficiently
• Categories
• Sorting
• Searching
• Graph algorithms
• Scientific computing matrix, number-theoretic,
  computational geometry, etc.

33
Internal force

• Mathematics
• Everything finally goes back to mathematics!
• Number theory
• Geometry
• Combinatorics
• Graph theory

34
A Good Team

• three factors crucial for being a good
  programming team
• Knowledge of standard algorithms and the ability
  to find an appropriate algorithm for every
  problem in the set
• Ability to code an algorithm into a working
  program
• Having a strategy of cooperation with your
  teammates

35
Quickly identify problem types

• In programming contests, you will be dealing with
  a set of problems, not only one problem.
• Problem types
• Mathematics (number theory, big integer, etc)
• Sorting
• Searching
• Simulation
• String processing
• Dynamic programming (DP)
• Graph
• Computational geometry
• Ad Hoc (i.e., no standard categories)

36
Analyze your algorithm

• Proof of algorithm correctness
• Time/Space complexity analysis for non recursive
  algorithms
• For recursive algorithms, the knowledge of
  computing recurrence relations and analyze them
  iterative method, substitution method, recursion
  tree method and finally, Master Theorem
• Given the maximum input bound (usually given in
  problem description), can my algorithm, with the
  complexity that I can compute, pass the time
  limit given in the programming contest?

37
Some rules of thumb

• Biggest built in data structure "long long" is
  263-1 91018 (up to 18 digits)
• If you have k nested loops running about n
  iterations each, the program has O(nk) complexity
• The best times for sorting n elements are
  O(nlog n)
• DP algorithms which involves filling in a matrix
  usually in O(n3)
• In contest, most of the time O(n log n)
  algorithms will be sufficient

38
Testing your code

• You wont get any credit by partially solving the
  problem.
• You need to be able to design good test cases
• Sample input-output given in problem description
  is by default too trivial to measure your code's
  correctness
• Before submission, you may want to design some
  tricky test cases first, test them in your own
  machine, and ensure your code is able to solve
  them correctly

39
Guidelines in designing good test cases

• Must include sample input, the most trivial one
• Must include boundary cases, what is the maximum
  n,x,y, or other input variables, try varying
  their values to test for out of bound errors
• For multiple input test case, try using two
  identical test case consecutively. Both must
  output the same result. This is to check whether
  you forgot to initialize some variables
• Increase the size of input. Sometimes your
  program works for small input size, but behave
  wrongly when input size increases.
• Tricky test cases, analyze the problem
  description and identify parts that are tricky,
  test them to your code.
• Dont assume input will always nicely formatted
  if the problem description didnt say so. Try
  inserting white spaces (space, tabs) in your
  input, check whether your code is able to read in
  the values correctly
• Finally, do random test cases, try random input
  and check your code's correctness

40
Producing Winning Solution

• Write down a game plan for what you're going to
  do in a contest round
• Read through all the problems first, don't
  directly attempt one problem since you may missed
  easier problem.
• Order the problems shortest job first, in terms
  of your effort
• Sketch the algorithms, complexity, the numbers,
  data structures, tricky details.
• Brainstorm other possible algorithms
• Do the Math! (space time complexity)
• Code it of course, as fast as possible, and it
  must be correct
• Try to break the algorithm - use special
  (degenerate?) test cases.

41
Coding a problem

• Only coding after you finalize your algorithm.
• Create test data for tricky cases.
• Code the input routine and test it (write extra
  output routines to show data).
• Code the output routine and test it.
• Write data structures needed.
• Stepwise refinement write comments outlining the
  program logic.
• Fill in code and debug one section at a time.
• Get it working verify correctness (use trivial
  test cases).
• Try to break the code - use special cases for
  code correctness.

42
Tips tricks for contests

• Brute force when you can, Brute force algorithm
  tends to be the easiest to implement.
• KISS Simple is smart! (Keep It Simple, Stupid
  !!! / Keep It Short Simple).
• Hint focus on limits (specified in problem
  statement).
• Waste memory when it makes your life easier
  (trade memory space for speed).
• Don't delete your extra debugging output, comment
  it out.
• Optimize progressively, and only as much as
  needed.
• Keep all working versions!

43
Tips tricks for contests (Cont.)

• Code to debug
• a. white space is good,
• b. use meaningful variable names,
• c. don't reuse variables, (we are not doing
  software engineering here)
• d. stepwise refinement,
• e. Comment before code.
• Avoid pointers if you can.
• Avoid dynamic memory like the plague statically
  allocate everything.
• Try not to use floating point if you have to,
  put tolerances in everywhere (never test equality)

44
Some Google interview questions

• Given a function which produces a random integer
  in the range 1 to 5, write a function which
  produces a random integer in the range 1 to 7.
• Find the intersection of 2 sorted integer arrays.
  What if one of them is huge? What if one of them
  is so huge, it can't fit in memory. How do you
  minimize the number of disk seeks?
• Given a string A, how do you find all the
  repeated substrings with minimum size of 2?
• Given N computers networked together, with each
  computer storing N integers, describe a procedure
  for finding the median of all of the numbers.
  Assume that a computer can only hold O(N)
  integers (i.e. no computer can store all N2
  integers). Also assume that there exists a
  computer on the network without integers, that we
  can use to interface with the computers storing
  the integers .

45
Example AB Problemhttp//acm.zju.edu.cn/onlinej
udge/showProblem.do?problemCode1001

• Time Limit1 second  Memory Limit32768 KB
• Description Calculate a b
• Input
• The input will consist of a series of pairs of
  integers a and b, separated by a space, one pair
  of integers per line.
• Output
• For each pair of input integers a and b you
  should output the sum of a and b in one line, and
  with one line of output for each line in input.
• Sample Input
• 1 5
• Sample Output
• 6

46
Example Solution
/ C code / include stdio.h int main()
int a, b while (scanf(d d, a, b) !
EOF) printf(d\n, ab)
return 0
/ Java code / import java.util.Scanner
public class Main public static void
main(String args) Scanner in new
Scanner(System.in) while
(in.hasNextInt()) int a
in.nextInt() int b in.nextInt()
System.out.println(a b)

47
Fundamental Problemshttp//acm.zjut.edu.cn

• 1167
• 1166
• 1174
• 1175
• 1176
• 1177
• 1178
• 1179

• 1181
• 1185
• 1190
• 1191
• 1187
• 1204
• 1208
• 1205
• 1044

48
Fundamental Problemshttp//acm.uva.es

• http//acm.uva.es/p/v1/100.html
• http//acm.uva.es/p/v101/10189.html
• http//acm.uva.es/p/v101/10137.html
• http//acm.uva.es/p/v7/706.html
• http//acm.uva.es/p/v102/10267.html
• http//acm.uva.es/p/v100/10033.html
• http//acm.uva.es/p/v101/10196.html
• http//acm.uva.es/p/v101/10142.html

49
3n1 Problem

• The 3n1 problem
• http//acm.uva.es/p/v1/100.html
• This is an outstanding unsolved problems in
  number theory, called 3n1 conjecture.
• Start with an integer n
• If n is even, nn/2 else n 3n1
• Repeat this process, terminating when n1.
• Its conjectured that this algorithm will
  terminate at n1 for every integer n.
• E.g.
• 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1
• The cycle length for 22 is 16.

50
3n1 problem

• Write a function to calculate the maximum cycle
  for integers between and including i and j

• Write a function to calculate the cycle length
  for integer i

void solve(int i, int j) int t, m, n int
length, maxlength if( i lt j) m i
n j else m j n i
maxlength 1 for(t m t lt n t)
length cycle_length(t) if (length gt
maxlength) maxlength length
printf("d d d\n", i, j, maxlength)
int cycle_length(int i) int length 1
while (i ! 1) if( i 2 0) i
igtgt1 else i iltlt1 i 1
length return length
51
The trip

• http//acm.uva.es/p/v101/10137.html
• A number of students are members of a club that
  travels annually to exotic locations.
• The group agrees in advance to share expenses
  equally, but it is not practical to have them
  share every expense as it occurs. So individuals
  in the group pay for particular things, like
  meals, hotels, taxi rides, plane tickets, etc.
• After the trip, each student's expenses are
  tallied and money is exchanged so that the net
  cost to each is the same, to within one cent. In
  the past, this money exchange has been tedious
  and time consuming.
• Your job is to compute, from a list of expenses,
  the minimum amount of money that must change
  hands in order to equalize (within a cent) all
  the students' costs.

52
The trip (Cont.)

• The Input
• Standard input will contain the information for
  several trips. There are no more than 1000
  students and no student spent more than
  10,000.00. A single line containing 0 follows
  the information for the last trip.
• The Output
• For each trip, output a line stating the total
  amount of money, in dollars and cents, that must
  be exchanged to equalize the students' costs.

Sample Input 4 15.00 15.01 3.00 3.01 0 Output
11.99
Sample Input 3 10.00 20.00 30.00 0 Output 10.00
53
The trip (Cont.)

• Its important to analyze the problem first.
• After you find the optimal way which can achieve
  the minimum amount of money that must change
  hands, writing the program will be very easy.
• Whats the difficulty of this problem?
• We need to equalize the costs as much as
  possible. That means
• if A pays the most, and A pays PA if B pays the
  least, and B pays PB,
• We need to have PB lt PA lt PB1

54
The trip (Cont.)

• Assume there are n students. We can calculate the
  total money.
• If the total money is a multiple of n, then we
  can equalize the costs. The problem is easy to
  solve.
• Example 1 10.00, 20.00, 30.00
• Total 60.00, average 20.00
• The first student receives 10.00 from the third
  student
• The second student doesnt need to do anything.
• The answer will be 10.00

55
The trip (Cont.)

• If the total money is not a multiple of n
• Let start from an example
• 1.10, 2.10, 3.10, 10.00
• Total 16.30 4x4.07 0.02
• The final cost should be 4.07, 4.07, 4.08, 4.08
• To minimize the amount of money change
• 1.10 ? 4.07 2.10 ? 4.07 3.10 ? 4.08 10.00
  ?4.08
• The answer will be 5.92
• Question do we need to sort the cost?