제출 #19960

#	제출 시각UTC-0	아이디	문제	언어	결과	실행 시간	메모리
19960	2016-02-25 07:50:23	gs13068	순열 (kriii4_T)	C++98	100 / 100	367 ms	8896 KiB

T

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#include <cstdio>
#include <algorithm>
const int p = 1000000007;
using namespace std;
int f(int x, int y)
{
  return y & 1 ? (long long)f(x, y ^ 1)*x%p : y ? f((long long)x*x%p, y >> 1) : 1;
}
int fac[1000001];
int inv[1000001];
int main()
{
  int i, j, n, m, r = 0;
  scanf("%d%d", &n, &m);
  fac[0] = 1;
  for (i = 1; i <= n + 1; i++) fac[i] = (long long)fac[i - 1] * i % p;
  inv[n + 1] = f(fac[n + 1], p - 2);
  for (i = n + 1; i >= 1; i--) inv[i - 1] = (long long)inv[i] * i % p;
  for (i = 0; i < n - m; i++)
  {
    j = fac[n - i];
    j = (long long)j * fac[n - m + 1] % p;
    j = (long long)j * inv[n - m - i - 1] % p;
    j = (long long)j * f(i + 2, p - 2) % p;
    r = (r + j) % p;
 
 
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• Subtask 1: 8 / 8
• Subtask 2: 92 / 92