count[s] will return true if the Key s is in the object.

So if the key s is in the object it will increase the value (++), else if will add it and put the value 1 (count[s] = 1)

yea me neither tell me if you get it

array indexing starts at 0 as the first item and goes up to array.length - 1, thus arr[array.length] is add a new item after the last one

Please, use spoiler flag next time.

i dont understand why num=num/2;

This is really a maths problem (and not an easy one), not a coding one. It says nothing about your abilities as a programmer.

Hey man, i basically googled summing consecutive numbers and found https://nrich.maths.org/summingconsecutive/solution, basically some kids doing some work for us :) Just read the article and you will get it.

I spent 10 hours+ figuring out a mathematical solution based on triangular numbers and the hint that a solution existed without iteration. Keep trying. I'm probably dumber ;-)