Solution 注意取模!!! Code #include<bits/stdc++.h> #define mod 1000000007 #define LL long long using namespace std; int n, a, b; LL mpow(LL a, LL b) { LL ans = ; , a = a * a % mod) ) ans = ans * a % mod; return ans; } LL fac[], inv[], l[], t[]; void init…