有点问题吧

The statement "Given a point p between 0 and s = a_1+a_2+...a_n, it
has at most (n-1)! ways to reach." looks suspicious. Think about 1,2,3. There are 4 sequences that reaches 3 ([1,2,3],[2,1,3],[3,1,2],[3,2,1]) and 4 > 2!