I was trying to solve the problem FTRIP Field Trip. I came to the conclusion that I have to calculate some binomial coefficients C(n,k). But the ranges were high. At the worst case I have to calculate C(1000,500). This obviously will not fit 64 bit int. I could use doubles, but even that will not be precise enough ( or so I thought ). I tried thinking of other solutions that didn’t involve binomial coefficient, but didn’t find any. If only I could calculate C(n,k) with enough precision then problem would be solved.

Then I went to the editorial to see how they handled the situation. They used double. Now I am confused. How will I determine if the double would be precise enough to get me AC? Is it because this problem has special judge that using double leads to AC?