给你两个正整数 n
和 limit
。
请你将 n
颗糖果分给 3
位小朋友,确保没有任何小朋友得到超过 limit
颗糖果,请你返回满足此条件下的 总方案数 。
示例 1:
输入:n = 5, limit = 2 输出:3 解释:总共有 3 种方法分配 5 颗糖果,且每位小朋友的糖果数不超过 2 :(1, 2, 2) ,(2, 1, 2) 和 (2, 2, 1) 。
示例 2:
输入:n = 3, limit = 3 输出:10 解释:总共有 10 种方法分配 3 颗糖果,且每位小朋友的糖果数不超过 3 :(0, 0, 3) ,(0, 1, 2) ,(0, 2, 1) ,(0, 3, 0) ,(1, 0, 2) ,(1, 1, 1) ,(1, 2, 0) ,(2, 0, 1) ,(2, 1, 0) 和 (3, 0, 0) 。
提示:
1 <= n <= 106
1 <= limit <= 106
i
which means 0 <= i <= min(limit, n)
.j
candies. Then 0 <= j <= limit
and i + j <= n
.n - i - j
candies and we should have 0 <= n - i - j <= limit
.i
, we have max(0, n - i - limit) <= j <= min(limit, n - i)
, each j
corresponding to a solution.
So the number of solutions for some i
is max(min(limit, n - i) - max(0, n - i - limit) + 1, 0)
. Sum the expression for every i
in [0, min(n, limit)]
.