CareerCup

I was given a questions during an interview which I was not able to solve, please help me in finding the solution.

Ques : - Divide the set in two partition such that both the partition has minimum difference of their sum. If we add an element to the left subset during partitioning than the value of that number will automatically increases by 1, but it will not increase by 1 if I add it to the right side. Find the minimum difference between both the subsets : -

ex :- {1,2,3,4,5}
 leftSubset = {3,4} , rightSubset = {1,2,5}
 effective sum of leftSubset = 3+4+2(number of elements)
 effective sum of rightSubset = 1+2+5 = 8
 difference of left and right = (9-8)=1 =, min difference

solution : (1,2,3} {4,5}

We need to make a string of size n. Each character of the string is either ‘R’, ‘B’ or ‘G’. In the final string there needs to be at least r number of ‘R’, at least b number of ‘B’ and at least g number of ‘G’ (such that r + g + b <= n). We need to find number of such strings possible.
For example,
n = 4, r = 1, b = 1, g = 1.
Output:
36