CodeForces 633E Startup Funding (概率)

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <vector>#include <set>using namespace std;#define N 2000030#define ls (i << 1)#define rs (ls | 1)#define md (ll + rr >> 1)#define lson ll, md, ls#define rson md + 1, rr, rs#define LL long long#define pii pair<int, int>#define mp make_pair#define fi first#define se secondint v[N], c[N];int n, k;int ans[N];double fac[N];double C(int x, int y) {return fac[x] - fac[y] - fac[x-y];}int main() {for(int i = 1; i < N; ++i) fac[i] = fac[i-1] + log(i * 1.0);scanf("%d%d", &n, &k);for(int i = 1; i <= n; ++i) scanf("%d", &v[i]), v[i] *= 100;for(int i = 1; i <= n; ++i) scanf("%d", &c[i]);for(int i = n; i >= 1; --i) {ans[i] = min(max(ans[i+1], v[i]), c[i]);}double x = 0;double res = 0;sort(ans + 1, ans + n + 1);for(int i = 1; i <= n - k + 1; ++i) {res += exp(C(n - i, k - 1) - C(n, k)) * ans[i];}printf("%.12lf\n", (double) res);return 0;}