Link- https://www.codechef.com/COHA2019/problems/BULLETS

I realise that by seeing others solutions that the answer will be Gaitonde if the XOR of all numbers is non-zero or Isa otherwise(if zero), but can anybody explain the logic behind it?

Itâ€™s the game of Nim in (a bit of a) disguise.

The reasons why the xor trick works is due to the Sprague Grundy Theorem.

Hackerrank have a Game Theory section with lots of nice practice problems

So quick! Did you take part in the contest? Anyway I was solving problems after the contest was over and I found the 5th problem easier then this one. I couldnâ€™t crack this.

No, that contest was too short for me The Hackerrank Game Theory section is full of Nim-style games, so I was primed to spot it quite quickly

This question is really a â€śyou have to know it (or at least Google it)â€ť - the Sprague-Grundy Theorem is not something people are likely to come up with in a 2 hour contest, and the results of the theorem are not at all intuitive.

@anon62928982 Yeah, this is the correct explaination.

I am the setter for the question, the editorial is Coming Soon !

How to solve the question Sartaj Drinks Gotchi?

Thanks for the links

Because I checked, Gaurav Sen has nice videos on Game Theory and Grundy Numbers. You may want to check that.

Thanks to you too