I was doing MARBLES https://www.codechef.com/problems/MARBLES question but I got stuck and dont know how to calculate the value of nCr ? Which method/concept to be used?
Have a try the formula
nCr = n! / r! * (n - r)!
nCr can be calculated by direct formula or you can use some optimization.
We know that nCr = nC(n-r) Hence choose min(r,n-r).
let value of nCr = 1
Then iterate i trough 1 to r and keep ans *= (n-i+1) and dividing in next step by i.
Go through the article below. Hope this helps.