For example, you want to calculate the sum of 1 to 100, you should not write:

var sum=0
for (var i=1;i<=100;i++) sum+=i
return sum

you only need write:

return 100*101/2

You need find out a formula ;-)

maybe you need an O(1) solution, the point of this kata is not calculate, is find a simple way to get the result.

and in fact, this kata did not need more calcute but need more thinking ;-)

perhaps you can paste your code here(Mark as having spoiler content) and ask someone to help you ;-)