标签:bsp com style while pac back size tar bit
#include <bits/stdc++.h> #define LL long long #define ULL unsigned long long #define mem(i, j) memset(i, j, sizeof(i)) #define rep(i, j, k) for(int i = j; i <= k; i++) #define dep(i, j, k) for(int i = k; i >= j; i--) #define pb push_back #define make make_pair #define INF 0x3f3f3f3f #define inf LLONG_MAX #define PI acos(-1) #define fir first #define sec second #define lb(x) ((x) & (-(x))) using namespace std; const int N = 1e6 + 5; const LL mod = 998244353; LL ksm(LL a, LL b) { LL res = 1LL; while(b) { if(b & 1) res = res * a % mod; a = a * a % mod; b >>= 1; } return res; } LL fac[N]; LL C(LL n, LL m) { return fac[n] * ksm(fac[m] * fac[n - m] % mod, mod - 2) % mod; } void solve() { LL n, k; scanf("%lld %lld", &n, &k); fac[0] = 1LL; for(LL i = 1LL; i <= n; i++) fac[i] = fac[i - 1] * i % mod; if(k == 0LL) { printf("%lld\n", fac[n]); return ; } if(k >= n) { puts("0"); return ; } LL ans = 0LL; LL flag = 1LL; rep(i, 0, n - k) { ans = (ans + flag * C(n - k, n - k - i) * ksm(n - k - i, n) % mod + mod) % mod; flag = -flag; } ans = 2LL * C(n, n - k) * ans % mod; printf("%lld\n", ans); } int main() { // int _; scanf("%d", &_); // while(_--) solve(); solve(); return 0; }
E. Placing Rooks (组合数学,经典容斥,思维)
标签:bsp com style while pac back size tar bit
原文地址:https://www.cnblogs.com/Willems/p/12817829.html