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HKOI Programming

HKOI Programming. HKOI Training Team (Intermediate) 2004-01-31. What you should learn from this lesson. How to solve a problem How to code faster How to test your program How to score more. Today’s flow. Competition Rules Problem Solving Coding Testing Tricks. Competition Rules.

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HKOI Programming

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  1. HKOI Programming HKOI Training Team (Intermediate) 2004-01-31

  2. What you should learn from this lesson • How to solve a problem • How to code faster • How to test your program • How to score more

  3. Today’s flow • Competition Rules • Problem Solving • Coding • Testing • Tricks

  4. Competition Rules • The winner is determined by • Fastest program? • Amount of time used in coding? • Number of tasks solved? • Highest score

  5. Scoring • Black-box Testing • Marks will be given if a program passes a certain test case • A test case is passed if the output • matches the expected one, or • satisfies certain criteria • No referral to source code

  6. The “OI” Programming Process • Reading the problem • Thinking • Coding • Testing • Finalizing the program

  7. Reading the problem • Usually, a task consists of • Title • Problem Description • Constraints • Input/Output Specification • Sample Input/Output • Scoring

  8. Reading the problem • Constraints • Range of variables • Execution time • NEVER make assumptions yourself • Ask whenever you are confused • Read EVERY word • Make sure you understand before going on

  9. Thinking • Classify the problem • Graph? Mathematics? Data Processing? … • Compare with some past problems • Any similarity? • For complex problems, divide the problem into smaller sub-problems

  10. Thinking • Draw diagrams • Consider special cases • Is the problem too simple? • Be suspicious, you may have overlooked something • Still no idea? Give it up… Try again later

  11. Designing the solution • Some points to consider • Execution Time (Time Complexity) • Amount of memory used (Space Complexity) • How to store data? (Data Structure) • Difficulty in coding

  12. Coding • Coding is just a small part in the competition • Less coding time means more time for thinking (which is more important) • FYI, usually I complete a program in 15 minutes • How to reduce code faster?

  13. Characteristics of OI programs • Simple Input/Output • Assumption: Data input format always matches specification • Short programs (usually < 100 lines)

  14. Common practices in OI-coding • No comments needed • Short variable names (usually 1-2 chars) • Less procedures / functions • Use of break, continue and goto • Hardcoding (Not recommended)

  15. Common practices in OI-coding • Use a slightly larger array than needed • Pascal users: use longInt instead of integer • Avoid real numbers (sometimes not possible) • Avoid long and complex expressions • Save and Compile frequently

  16. Testing • Sample Input/Output • “A problem has sample output for two reasons: • To make you understand what the correct output format is • To make you believe that your incorrect solution has solved the problem correctly ”

  17. Testing • Create some simple input yourself (by hand) • Boundary cases • “Large” input • Test for execution time and integer overflow • Tricky cases

  18. Debugging • Print values of important variables to screen and/or files • Print messages to screen and/or files • Use debugger • FreePascal IDE debugger • GDB

  19. Finalizing • Check I/O filename • Check output format • Any trailing spaces? • Correct source/executable name? • Is the executable updated?

  20. Tricks • Quick and dirty ways to get marks • Usually, 10-20% of total marks are allocated to simple test cases • Write programs that handles these cases ONLY • Use only when you have totally no idea on a task or time is running out

  21. Tricks • “No solution” • Sample Input/Output • Special cases • Hardcoding • Stop the program before execution time runs out

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