# How to understand ICL21 Problem A

Its clearly meant to be an O(k ^ 2 * m) dp, but the question is really vague on:

• Where you start (always first position, or any?)

• What is a “move”

• Is picking up two tachyons at the same position a single move?

• Can two tachyons exist at the same position and the same time? If so can you collect both?

• If I pick up some tachyons and then don’t move from my initial position, is this considered to be 0 or 1 moves.

Like I sat there for 30 mins after solving B to E trying to figure out which one they meant and eventually just submitting as many as possible.

Now that the contest is over, can anyone please explain the correct interpretation.

2 Likes

@paulkallumkal
Sorry for off-topic. But I think the constraints for the first problem were wrong. Value of F was more than 2 \times10^5 for some test-cases. ASSERTION. This wasted a lot of time.

Edit: misread F as N in the previous comment, changed the reply.

Ok, that might explain why I got 4-5 SIGSEVs on the last case.

But I finally got accepted by changing it to n = 10^{6} which makes no sense.

Wow, this doesn’t make sense at all , something’s off

The fairly intuitive part is you start before the first stop.
A move can be defined as picking a tuple. The question was about choosing up to M tuples from the list to maximise the amount of tachyons collected.

Apologies for vagueness in various parts of the question

Hi, sorry about that. The final test case was added to force a TLE on naive approaches, but we forgot to change the constraints afterwards causing the confusion. It’ll be rejudged without the final case.

when will be problems added to the practice session?