update the pretests scores here-https://docs.google.com/spreadsheets/d/1DRZe_LyIdkXZkMxHtgklhfskpmh-Hudq8v-nT8w4EIs/edit?usp=sharing

# ZCO2020 cutoff and score

Which class you are of?

I got 200 but with great difficulty

Interesting. But I feel the intended solution would use representing numbers in binary.

For example if p=4, and I am asked which number is in index idx equal to, say, 3, then we can simply to do following:

- Represent idx in binary form in p digits. Add leading 0's if needed. In our case, 3 \equiv 0011_2 .
- Set answer variable, ans to 0.
- If the last bit in idx is 1, then
`ans=ans*2+1`

. Else,`ans=ans*2`

. - Divide idx by 2 and repeat step 3-4 for a total of p times.

The intuition behind it is:

- If a number is even, it is placed in the left subarray.
- If we take all the elements in left subarray, and now focus on them. They all are even, obviously. Divide them by 2 now. Out of all these numbers, the numbers which are still even go to left half of this subarray, rest goto right half.
- Similarly we ca carry on and argue for all further subarrays.

```
repeat p times
if ( (idx&1)==1)
ans=(ans<<1)|1;
else
ans<<=1;
idx>>=1;
```

Sir, my logic was same but different

Expected cutoff this time ?

Also what do u guys think. Was the ZCO easier this year or harder

What’s your score

Not good, messed up a lot idk what happens to me in onsite competitions

I think cutoff is going to be 100

To high for ZCO cutoff

I have stopped using this statement from ZIO 2020 onwards. Anything Is possible

Can anyone share the problems of zco.

my score is 0

Who all are getting 100pts ++ ?

I was only able to solve the first sub task of the first problem (just implement the algorithm in the question) . I thought memoization must be used to make the recursive algorithm faster. But I kept getting RTE. Spend too much time there and so I had only 15 minutes for last problem (I was confident about memoization so I thought if I implemented it I might get 100) and I did not solve the second problem. Getting 20. Hopefully, I will qualify for INOI. Can someone explain how to get rid of TLE in the first problem. I just came home and I think we have to use DP for the second.

That’s the same as reversing the binary representation of idx (taking into account leading zeroes of course), right?

I didn’t attend ZCO, but I think you should have just solved the easiest subtasks on both the problems, the brute force ones. That would surely be enough to qualify.

Yes, if you use exactly p digits and take into account the leading zeroes, I too feel that its just reversing the bits.

I just used a while loop and a for loop(for test cases).

I spent all of my time on this problem

But at least I got 100!

How many people qualify for ZCO on average?

Also, can anyone share the solution for P2?

About 150 qualify for each, ZIO and ZCO

Could someone tell me where I can see the questions?