contest algorithms january 2016 dr. andrew davison dept. of computer engineering prince of songkla...

Contest Algorithms 1

Contest AlgorithmsJanuary 2016

Dr. Andrew DavisonDept. of Computer Engineering

Prince of Songkla [email protected]

1. Introduction

http://fivedots.coe.psu.ac.th/Software.coe/ContestAlgs/


Knowledge of Java e.g. 241-211. Object Oriented Programming

Intro to big-Oh and algorithms e.g. 241-303 / 242-313 Discrete Mathematics 242-310 Intro to Algorithms and Complexity

Prerequisites


Makes you a better programmer and thinker in many situations

Develop skills that will set you apart in the workforce

It's fun

Why Compete?

ACM-ICPC

ICPC is a tiered competition among teams of students representing institutions of higher education.

Teams compete in local contests, then Regional Contests, from which top scoring teams advance to the ACM-ICPC World Finals

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Format: 3 people 1 computer 5 hours 10 problems 25 page team reference document

Rules: http://www.acmicpc-thailand.org/asia/2015/contest https://icpc.baylor.edu/

What is ACM?

ACM: Association for Computing Machinery http://www.acm.org/ the world’s largest educational and scientific computing

society

ACM ICPC ACM International Collegiate Programming Contest http://en.wikipedia.org/wiki/ACM_International_Collegiate_Prog

ramming_Contest

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http://www.acm.org/

http://en.wikipedia.org/wiki/ACM_International_Collegiate_Programming_Contest

http://en.wikipedia.org/wiki/ACM_International_Collegiate_Programming_Contest


Know your teammates Delegating problems to each other

Share the computer time effectively Create test cases for each other Communicate well Pair programming

Teamwork

Producing Winning Solution

Write a team programming plan Read through all the problems first Order the problems: shortest first, in terms of your effort Outline the algorithms,data structures, tricky details Do the math! (space & time complexity) Write the code to be fast and correct Try to break the algorithm - use tricky test cases

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Problem description/statement can be unnecessarily long or misleading

Input and output description usually very precise assume that all input will be formatted like this

Sample input and output one or more inputs and expected outputs

Problem Statement/Recipe


Searching / Sorting Dynamic programming Greedy Maths

number theory, big integer, etc

String processing Computational geometry

Complete search also known as brute force backtracking

Divide and conquer Graph

traversal minimal spanning tree

(MST) shortest paths maxflow

Quickly identify problem types

Coding a Problem

Brute force algorithm tends to be the easiest to implement.

KISS: Keep It Short & Simple Use more memory space if it makes the code faster Don't delete your debugging output, comment it out Optimize step-by-step, and only as much as needed Keep all working versions

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Only start coding after you decide on the algorithm Code the input routine and test it

write extra output routines to show data

Code the output routine and test it Write comments outlining the program logic Code and debug one section at a time

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Coding style: white space is good use meaningful variable names develop code in small steps add useful comments

Try not to use floating point, or be aware of inaccuracy e.g. instead of $12.34, use 1234 cents double x = ...;if (x == 4) // badif (Math.abs(x-4) < 1e-9) // good

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Read the problem Decide whether or not you know how to solve it

If you think you can solve it: Parse the input Write the code Check that the program works on the sample input/output Submit!

If you're not sure, move onto the next problem

Steps to solving a problem


import java.io.*;

public class Main { public static void main(String[] args) // throws Exception { BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); int nCases = Integer.parseInt(in.readLine()); for (int caseNum = 0; caseNum < nCases; caseNum++) { // Parse the input number int n = Integer.parseInt(in.readLine()); :

Parts to a (OLD style IO) Program

INPUT &PARSING

standard name


: // Calculate the answer n *= 567; n /= 9; n += 7492; n *= 235; n /= 47; n -= 498;

// Digit in the tens column int tens = (n / 10) % 10;

System.out.println(tens); } } // end of main()

} // end of Main class

PROCESSING /ALGORITHM

OUTPUT


public static int parseInt(String s) { if (s == null) return 0; try { return Integer.parseInt(s); } catch (NumberFormatException ex){ System.out.println(s + " could not be parsed as an int; using 0"); return 0; } } // end of parseInt()

Parsing String to int

Scanner s = new Scanner(System.in);while (s.hasNextLine()) { String line = s.nextLine(); // process line ...}

Console r = System.console();String line = null;while ((line = r.readLine()) != null) { // process line ...}

Two modern ways

use this one

Contest Algorithms: 1. Intro 20

import java.util.Scanner;

public class ScannerAdd // use Main in contests{ public static void main(String[] args) throws Exception { Scanner s = new Scanner( System.in ); System.out.print("Enter first integer: "); int x = s.nextInt(); System.out.print("Enter second integer: "); int y = s.nextInt(); s.close(); System.out.println("Adding gives: " + (x+y) ); }} // end of ScannerAdd class

Adding Two Numbers see ScannerAdd.java


Compile & Execute


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

public class AddDoubles // use Main in contests{ public static void main(String[] args) throws Exception { double total = 0; Scanner sc = new Scanner(System.in);

while ( sc.hasNextDouble() ) total += sc.nextDouble();

sc.close(); System.out.println("Total = " + total ); }} // end of AddDoubles class

Adding any number of Numberssee AddDoubles.java


Compile & Execute

ctrl-D and<enter>

inaccuracy infloating point


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

public class UseGraph // use Main in contests{ public static void main(String[] args) throws Exception { Scanner sc = new Scanner(System.in); // Scanner sc = new Scanner(new File("graphData.txt")); // for testing

int numVs = sc.nextInt(); int[][] adjMat = new int[numVs][]; // use numVs as no. of rows for (int i = 0; i < numVs; i++) { adjMat[i] = new int[numVs]; // create ith row array for (int j = 0; j < numVs; j++) // fill row adjMat[i][j] = sc.nextInt(); } :

Fill an Integer Matrix see UseGraph.java


// print it out for (int i = 0; i < numVs; i++) { for (int j = 0; j < numVs; j++) System.out.printf(" %3d", adjMat[i][j]); System.out.println(); } System.out.println(); } // end of main()

} // end of UseGraph class


Compile & ExecuteReading from graphData.txt


6 0 10 0 0 100 0 10 0 7 0 8 0 0 7 0 9 0 00 0 9 0 20 5100 8 0 20 0 0 0 0 0 5 0 0

graphData.txt

Reading Data Using Scanner

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java.util.Scanner

+Scanner(source: File)

+Scanner(source: String)

+close()

+hasNext(): boolean

+next(): String

+nextByte(): byte

+nextShort(): short

+nextInt(): int

+nextLong(): long

+nextFloat(): float

+nextDouble(): double

+useDelimiter(pattern: String): Scanner

Creates a Scanner that produces values scanned from the specified file.

Creates a Scanner that produces values scanned from the specified string.

Closes this scanner.

Returns true if this scanner has another token in its input.

Returns next token as a string.

Returns next token as a byte.

Returns next token as a short.

Returns next token as an int.

Returns next token as a long.

Returns next token as a float.

Returns next token as a double.

Sets this scanner’s delimiting pattern.


Almost the same as C's printf(). The main formating operations:

Java's printf()

Format specifier Description

%d Displays a decimal (base 10 ) integer

%f Display a floating point value in decimal format

%e or %E Display a floating point number in exponential notation

%c or %C Display characters%s or %S Display Strings%b or %B Display boolean values%% Display a % sign


1 page quick reference: https://www.cs.colostate.edu/~cs160/.Fall15/resources/

Java_printf_method_quick_reference.pdf

More words, but still 1 page: http://www.javawithus.com/tutorial/displaying-text-using-

printf-method

More information on printf


import java.util.Scanner;

public class Main { // save as Main.java public static void main(String[] args) { Scanner in = new Scanner(System.in); int i = in.nextInt(); double d = in.nextDouble();

String s = in.next(); // There is no nextChar(), use next() and charAt() char c = s.charAt(2); // third char // Read whole line (or rest of the line past '\n') String line = in.nextLine(); System.out.printf("%4d, %6.2f, %s, %c\n", i, d, s, c); // Use %f for double (not %lf) // Don't forget to print the '\n' }}

Template for ICPC Online Judge

https://www3.ntu.edu.sg/home/ ehchua/programming/ icpc/icpc_getting_started.html

see Main.java

Analyze your algorithm

Is your algorithm correct?

What is its time/space complexity?

Given the maximum input (usually given in the problem), can your algorithm stay inside the time limit for the contest?

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Some rules of thumb

The biggest Java integer data structure long can store 263-1 ≈ 9*1018 (up to 18 digits)

If you have k nested loops, each doing about n iterations, then the program has O(nk) runtime

The best times for sorting n elements is O(n log n) quicksort, mergesort use Java’s Arrays.sort()

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Contest Algorithms:12. Maths 35

Java Primitive Types

More info:https://docs.oracle.com/javase/tutorial/java/ nutsandbolts/datatypes.html

2 x 109

9 x 1018


Dynamic programming algorithms involving a table/matrix usually have O(n3) runtime

Aim to use O(n log n) algorithms e.g. binary search Java’s Array.binarySearch()

Testing your code

The sample input in the problem description is usually too simple for testing

Design tricky test cases, test them on your machine. Boundary cases Big input Badly formatted input Random test cases

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Submission Error (SE) Output Limit Exceeded (OL) Restricted Function (RF)

There are many ways to fail:

Presentation Error (PE) Wrong Answer (WA) Compile Error (CE) Runtime Error (RTE) Time Limit Exceeded (TLE) Memory Limit Exceeded

(MLE)

Judged code

Contest Algorithms


Accepted (AC) – Congratulations!

Accepted (PE) – Your program has a minor presentation error, but the judge is letting you off with a warning.

Stop here and declare victory!

Presentation Error (PE) – Check for spaces, left/right justification, line feeds, etc.

Meanings


Wrong Answer (WA) – Your program returned an incorrect answer to one or more secret test cases.

Compile Error (CE) – The compiler could not figure out how to compile your program.

The resulting compiler messages will be returned to you. Warning messages are ignored by the judge.

Runtime Error (RTE) – Your program failed during execution due to a segmentation fault, floating point exception, or similar problem.

Check for invalid pointer references or division by zero.


Submission Error (SE) – You did not correctly specify one or more of the information fields, perhaps giving an incorrect user ID or problem number.

Time Limit Exceeded (TL) – Your program took too much time on at least one of the test cases, so you likely have a problem with efficiency.

Memory Limit Exceeded (ML) – Your program tried to use more memory than the judge’s default settings.


For Java, the judges compile and execute your code using:

javac -encoding UTF-8 -sourcepath . -d . $* java -client -Xss8m -Xmx1024m $*

see https://icpc.baylor.edu/worldfinals/programming-environment

max heap sizefor object creation

thread stack sizefor storing its localexecution state


Output Limit Exceeded (OL) – Your program tried to print too much output, perhaps trapped in a infinite loop.

Restricted Function (RF) – Your source program tried to use an illegal system function. Probably a file operation.


Verdict by Language

from "Programming Challenges", Skiena, 2003;Java only allowed 1 year before


https://github.com/alexjbest/icpc-tcr University of Warwick TCR docs

https://github.com/i8r/icpc-tcr University of of Lübeck, Germany

Java Team Contest Reference Docs


Each contestant may bring a copy Up to 25 pages of ref materials, single-sided, letter

or A4 size, with pages numbered in the top right-hand corner and your university name in the top left-hand corner.

It may include hand-written comments and corrections on the fronts of pages only.

In a notebook or folder with the name of your institution on the front

TCR Doc Rules


Write code using a programming font in a text editor with color highlighting:

e.g. Source Code Pro https://github.com/adobe-fonts/source-code-pro

e.g. Notepad++ https://notepad-plus-plus.org/

Use fineprint printer driver to print 4 or 8 pages/sheet: http://fineprint.com/fp/

Generating a TCR Doc


Do not combine all the code files into one it makes it harder to change, test, regenerate the TCR

Install the "Print all" plugin into Notepad++ Go to Plugins -> Plugin Manager -> Show Plugin Manager,

then click on Available, then go down to Print all, check it, and install


https://www3.ntu.edu.sg/home/ehchua/programming/icpc/icpc_getting_started.html

http://www.ahmedshamsularefin.id.au/ acm-icpc/tutorials/16-links

great collection of links

https://en.wikipedia.org/wiki/ ACM_International_Collegiate_Programming_Contest

links to blogs, training

ICPC Help


Talking about programming contests only get you so far Past problems:

https://icpc.baylor.edu/worldfinals/problems

UVa Online Judge http://uva.onlinejudge.org

TopCoder http://topcoder.com

Project Euler http://projecteuler.net/

Practice

Available Online Judges (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-challenges.com)

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http://acm.uva.es/p

http://acm.timus.ru/

http://acm.sgu.ru/

http://acm.zju.edu.cn/

http://acm.zjut.edu.cn/

http://cii-judge.baylor.edu/

http://acm.pku.edu.cn/JudgeOnline/


TopCoder Weekly online individual competitions

Google Code Jam

Internet Problem Solving Competition Annual, fun, diferent style of problems

IOI, USACO

Other Programming Contests


Competitive ProgrammingSteven and Felix Halim, Third Edition

http://cpbook.net/

Programming ChallengesSteven S. Skiena and Miguel Revilla

http://www.programming-challenges.com/

Textbooks




From Baylor to BaylorMiguel A. Revilla

https://icpcarchive.ecs.baylor.edu/


Intro to Java Programming, Comprehensive, 10th ed.Y. Daniel Liang

http://www.cs.armstrong.edu/liang/intro10e/

Topics 2D arrays, String, BigInteger, bitwise ops,

regexs Generics, Collections (lists, stack, queues,,

sets, maps) Sorting, searching graph algorithms (2 chapters)


Algorithms, 4th ed.Robert Sedgewick, Kevin Wayne

http://algs4.cs.princeton.edu/

Introduction to Algorithms, 3rd ed.Thomas Cormen, Charles Leiserson, Ronald Rivest, Clifford Stein

lots of resources online; see video section


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http://www.chulabook.com/http://www.cp.eng.chula.ac.th/~somchai/books/

โครงสร�างข้�อม�ลและอ�ลกอรทึ�ม Data Structures and Algorithms)

ผู้��แต่�ง : ส"ธิ์# พงศาสก"ลช�ย & ณั�ฐพงษ์�วิาร#ประเสรฐhttp://ktpbook.com

MIT 6.046J / 18.410J Intro. to Algorithms, Fall 2005 http://ocw.mit.edu/6-046JF05

original course website for Cormen book

http://videolectures.net/mit6046jf05_introduction_algorithms/

video and slides side-by-side

http://www.catonmat.net/category/introduction-to-algorithms

notes taken while watching the videos

Videos


Skiena's Algorithms Lectures http://www3.cs.stonybrook.edu/~algorith/video-lectures/ 1997, 2007, 2012


Eclipse tutorials: http://eclipsetutorial.sourceforge.net/

totalbeginnerlessons.html 16 videos uses v3.3 (current is 4.5) from 2007

Various Youtube videos: Eclipse IDE Tutorial, luv2code (many videos) Eclipse IDE Tutorial, Norm Krumpe

contest algorithms january 2016 dr. andrew davison dept. of computer engineering prince of songkla...

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