ICHB Selection Contest '17 (Mirror)

Welcome to the mirror of the ICHB Selection Contest. This contest is used for the selection of the junior team for the International Autumn Tournament in Informatics.

The problem writers for this contest are WallE256 and casikun.

This contest will be unrated for all participants.

Before the contest date, you may wish to check out the tips and help pages.

This contest will consist of 3 problems.

Some problems offer partial marks in the form of subtasks. If you cannot solve a problem fully, we encourage you to go for these partial marks.

You will have 4 hours to complete the contest. After the contest window begins, you may begin at any time. Once you enter the contest, your personal timer will start counting down and you will be able to submit until 4 hours from when you started, or until the hard deadline, whichever comes first.

After joining the contest, you proceed to the Problems tab to begin. You can also go to Users if you wish to see the rankings.

We have listed below some advice as well as contest strategies:

  • Start from the beginning. Ties will be broken by the sum of times used to solve the problems starting from the beginning of the contest. The last submission time of your highest score will be used.
  • It is not guaranteed that the problems will be in order of increasing difficulty. Reading all of the statements is recommended.
  • Remove all extra debugging code and/or input prompts from your code before submitting. The judge is very strict — most of the time, it requires your output to match exactly.
  • Do not pause program execution at the end. The judging process is automated. You should use stdin / stdout to perform input / output, respectively.
  • It is guaranteed that all the problems will be solvable with C++.


Problem Points AC Rate Users
ICHB Selection Contest '17 Problem 1 - Airship Fights 10p 0.0% 0
ICHB Selection Contest '17 Problem 2 - Black Star's Visit 7p 7.6% 27
ICHB Selection Contest '17 Problem 3 - Parallel Universe 12p 16.1% 43


  • 2
    0xc3  commented on Nov. 12, 2017, 2:08 p.m. edited

    In the second problem, which numbers count as horizontally symmetrical? For example, does 1 count as symmetrical?

    • 0
      WallE256  commented on Nov. 12, 2017, 2:36 p.m.

      For horizontally symmetrical, the digits considered are 0, 3, and 8. For vertically symmetrical, the number need to be palindromic. (When the length is odd, the middle digit is ignored. Other than that, the description in the statement is still valid.)