折戟沉沙

题目链接 思路:先考虑只有k的请况,设f[i]为出现i种颜色的种数 k⋅(k−1)n−1=∑i≤kC(k,i)⋅f(i)k \cdot (k - 1)^{n - 1} = \sum_{i \leq k} C(k, i) \cdot f(i) 套二项式反演即可#include<iostream>#include<cstdio>#include<cmath>#include<cstring>