组合数学DP 发表于 2021-05-20 更新于 2021-09-10 组合数学DP一个挺有意思的题目 https://cses.fi/problemset/task/1717 There are n children at a Christmas party, and each of them has brought a gift. The idea is that everybody will get a gift brought by someone else. In how many ways can the gifts be distributed?