To solve this problem, I used biteset. The size of the bitset should be at least $$$10^4$$$. I used $$$10$$$ so that it's easy to debug. At the end I forgot that the size of bitest should be changed and submitted this code.The Verdict should be Wrong Answer/ Run time error. But it got Accepted.

Does anyone know the reason behind this?

I solved this problem in CF #705.

But it failed system testing showing

TLE code

Accepted code after contest

If we compare this two submissions-

This is the only difference.

The main thing is I used cerr for debugging and it got TLE.

Can anyone explain Why did it happen?