# [3428. Maximum and Minimum Sums of at Most Size K Subsequences](https://leetcode.com/problems/maximum-and-minimum-sums-of-at-most-size-k-subsequences/) **参考资料:** * [贡献法+组合数学+递推优化(Python/Java/C++/Go)](https://leetcode.cn/problems/maximum-and-minimum-sums-of-at-most-size-k-subsequences/solutions/3051549/gong-xian-fa-zu-he-shu-xue-pythonjavacgo-0jod/) 代码就不贴了,主要包括一些固定写法: 1. pow方法的自定义 2. 如何预处理n!和(n1!)^(-1),两者之间的转换INV_F[MX - 1] = pow(F[MX - 1], MOD - 2) 3. 对称,a[i]在sub-sequences为最大值的数目等于a[n - i - 1]在sub-sequences为最小值的数目 4. 代码完成