Preface

• TOKI KSN Open Contest 2021 is an open competition mirroring the National Science Olympiad in Informatics 2021 in Indonesia (KSN 2021 Bidang Informatika in Bahasa Indonesia).
• KSN Informatika is a national olympiad in informatics for high school students. It is one of the stages required for Indonesian students to represent Indonesia in IOI (International Olympiad in Informatics)
• The problemset is the same as the problemset in KSN 2021 Bidang Informatika and will be given in both Bahasa Indonesia and English.
• The contest will be held on TLX (TOKI Online Judge) (you may need to register for a TLX account if you do not have one).
• If you have any questions please contact sc-ksn-2021@googlegroups.com.

Rules Overview

• There will be one trial session and 2 (two) competition days.
• Result of the trial session does not affect scoring.
• There will be 3 (three) problems on each day to be solved in 5 (five) hours.
• Each contestant may submit up to 50 submissions for each problem. This limit may be increased for some problems.
• The supported programming languages are C and C++.
• During the competition, each contestant can only see their own scores.

Schedule and Technical Details

• The contests will be held at the following time ranges:
• Day 0: 7 November 2021 09:00 - 8 November 2021 01:30 UTC (trial session)
• Day 1: 8 November 2021 06:30 - 9 November 2021 01:30 UTC

• Day 2: 9 November 2021 06:30 - 10 November 2021 01:30 UTC

• Each contestant can select any 5-hour window within the time range to do the contest for each competition day.
• All three contests are now available on TLX. Please register in those contests.
• Each contestant may start the contest any time within the time range, by clicking the “start” button.
• There will be no additional time given if a contestant starts the contest in less than 5 hours before the contest ends.
• The open contest does not support clarifications, but all important announcements from the original contest will be broadcast as well.

Problems Types

• There are 3 possible problem types. Some problem type might not be tested.

• Batch problems:
  • The most common problem type.
  • Given an input, contestants write a program that reads input from stdin and writes output to stdout.
  • The program must run within the given time and memory limits.
  • Example: Online Ojek, OSN 2018
• Interactive problems:
  • Contestants write a program that interacts with judge’s program: judge’s program writes to stdout and is given as the stdin for contestant’s program, then contestant’s program writes to stdout and is given as the stdin for judge’s program, and the interaction continues until a given goal is reached.
  • Contestant’s program must output the answer within the given time and memory limits.
  • Example: Detecting Gold, OSN 2019
• Output-only problems:
  • Contestants will be given all the input test cases.
  • Contestants submit output for each input test case.
  • Contestants do not have to write a program; the outputs may be solved manually.
  • Example: OSN Excursion, OSN 2019.

Problem Scoring

• There are two types of scoring: standard and creative.

• Creative problems will be stated explicitly in the problem description.

• Standard scoring:
  • For batch and interactive problems:
    • A problem consists of multiple subtasks with various points.
    • A subtask consists of multiple test cases that are grouped into some test groups.
    • A submission gets a subtask’s points if it solves all of its test groups.
    • To solve a test group, a submission has to solve all of its test cases.
    • A problem may have open subtasks where the test cases are given to contestants.
  • For output-only problems:
    • A problem consists of multiple test cases with various points.
    • A submission gets the test case’s points if it produces the correct output.
• Creative scoring:
  • The scoring formula will vary for each problem and will be explicitly stated in the problem description.
  • Example:
    • Batch: Membaca, OSN 2012.
    • Interactive: Finding Balls, KSN 2020.
    • Output-only: National Defence, KSN 2020.

Contestant Scoring

• For batch and interactive problems:
  • On creative scoring, for each submission, the score of a subtask is the minimum score among all its test cases.
  • A subtask final score is the maximum of its score among all submissions.
  • Contestant’s score for a problem is the sum of all its subtasks final score.

  For example, if the first submission got 30 points for the first subtask and 0 points for the second subtask, and the second submission got 0 points for the first subtask and 40 points for the second subtask, then the contestant’s score for the problem is 70 points.

• For output-only problems:
  • A test case final score is the maximum of its score among all submissions.
  • A contestant’s score on a problem is the sum of all its test cases final score.
• A contestant’s total score is the sum of all of problems score on both competition days.
• Contestants will be ranked by the total score (descending).
• Two contestants with the same total score will achieve the same rank.
• Submission time will not affect contestant rank at all.

Grading System

• TLX will be used as the grading system.
• Source code limit for each submission is 300 KB.
• For each test case, the grader will output one of:
  • AC (Accepted): program solved the problem within the given time and memory limits.
  • WA (Wrong Answer): program stopped within given time and memory limits, but produced the wrong output.
  • RTE (Runtime Error): program crashed or exceedeed the memory limit.
  • TLE (Time Limit Exceeded): program exceeded the time limit.
  • Skipped: test case is not graded because there was a test case in the same subtask that was not solved.