It's not the easiest problem and I don't know good solution, but if I was on the olympiad and would have to solve the problem, I would just precalculate the answer.

a difficult combinatorics problem.

x1 + x2 +... + x10 = S

with limitation:  xi between ? , ?

Need to fill an array COUNT[1..9][0..81] and answer is COUNT[9][S]
Exclusion: if S == 1, then answer is 10

Edited by author 30.09.2014 22:13