Reactive and Output-Only HKOI Training Team 2006 Liu Chi Man (cx) 11 Feb 2006

Reactive and Output-OnlyReactive and Output-OnlyHKOI Training Team 2006

Liu Chi Man (cx)11 Feb 2006

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Outline

• Reactive tasks (a.k.a. interactive tasks)

• Output-only tasks (a.k.a. open test data tasks)

• Scoring methods

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Traditional tasks

• Read input, write output

• Static input

• Problem: Add Two Numbers• Input: Two integers per line• Output: For each input line, add the two integers

and output the sum on one line

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Add Two Numbers

• Algorithm One• while not end of input do

read integers from input

write sum to output

• Algorithm Two• read all integers into an array

compute all sums

write all sums to output

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Interactivity

• Problem: Guess The Number• My lucky number is an integer between 1 and N• Guess until you get the correct answer• After each guess I will tell you whether your guess

is too big or too small or correct

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Interaction via provided libraries

• Function calls

• Examples:• N := GetN(); / N = GetN();• MakeGuess(7);

• Task description contains sufficient instructions

• Using a library• Pascal: uses mylib;• C/C++: #include "mylib.h"

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Interaction via standard I/O

• I/O method same as traditional tasks

• IMPORTANT• Make sure you read and write in the correct order

specified in the task description

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Nature of reactive tasks

• Black-box testing

• Two-person games

• Updates and queries

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Black-box testing

• Use queries to reveal hidden information

• Examples include• Guess The Number• Mastermind

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Two-person games

• Write a program to play a game against the judging program

• Examples include• Tic-tac-toe• Nim (match-picking)

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Updates and queries

• Processing of a set of data

• “Update” command• Modify the set of data

• “Query” command• Ask for some information about the data

• A Query must be answered before next command is revealed

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Strategies

• Black-box testing• Bisection, trisection, etc.

• Two-person games• Minimax method (dynamic programming speed up)

• Updates and queries• More advanced data structures, e.g. disjoint sets

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Output-only tasks

• All input test cases are given to you

• You are required to submit corresponding output files for these inputs

• No source code, executable required

• Usually optimal (best) answers are very difficult to obtain• Partial scoring

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Nature of output-only tasks

• “Hard” problems• Optimal solutions not likely to be found within

minutes• For the precise definition of “hardness”, look

forward to “[Talk] Introduction to Complexity Theory”

• “Semi-manual” problems• Some of the test cases designed for you to solve by

hand or wicked methods

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Strategies• Manual inspection of all test cases

• Make sure you don’t miss those easy inputs

• Go for suboptimal solutions• Greedy, heuristics, random, etc.

• Fully utilize your resources• Hours of CPU time• Plentiful memory• Other tools (calc, sort, factor, bc, graphics software,

games, etc.)

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Effort vs. Score

Effort

Score

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1 Task = 10 Tasks!

• Sometimes test cases are designed so that each one has some special properties

• Different properties may lead to different solving methods

• 1 task, T programs• T is the number of test cases

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Conclusion

• 1 to 2 per competition (6 tasks in total)

• Reactive tasks are more popular than output-only tasks

• In general, it is easier to score high marks in reactive tasks than output-only tasks

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Frequencies

React Output React Output

IOI’00 1 0 NOI’00 0 0

IOI’01 3 1 NOI’01 0 0

IOI’02 1 1 NOI’02 1 1

IOI’03 2 1 NOI’03 1 1

IOI’04 0 0 NOI’04 1 1

IOI’05 1 0 NOI’05 0 1

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Scoring methods

• How are marks given for each test case?

• All-or-nothing• Correct – full; incorrect – zero

• Partial• You may get something between full and zero

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Partial scoring

• Multiple parts• Example: If you get the first integer wrong, you get

0%; if you get the first integer correct, you get 30%; if you get both integers correct, you get 100%

• Suboptimal award• Example (maximization): Let A be the optimal

answer and B be your answer; your score is (B/A) 100%

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Partial scoring

• Number of queries (Reactive: black-box testing)• Fewer queries, higher score

• Usually an explicit formula for score calculation is given

• Some of the variables in the formula may be unknown to you, however• “Your answer is compared to our answer”• Our refers to the judges

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Relative scoring

• Your answer is compared to the best answer among all contestants• If nobody else attempts that task, you win