Submission #1781024

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Source Code Expand

#include<bits/stdc++.h>

using namespace std;


typedef long long int64;
const int mod = 1777777777;

inline int64 modPow(int64 x, int64 n)
{
  if(n == 0) return (1);
  int64 ret = modPow(x, n / 2);
  (ret *= ret) %= mod;
  if(n & 1) (ret *= x) %= mod;
  return (ret);
}

inline int64 modInv(int64 a)
{
  return (modPow(a, mod - 2));
}

inline int64 modCombination(int64 n, int k)
{
  int64 res = 1;
  for(unsigned long long i = 1; i <= k; ++i) {
    (res *= n-- % mod) %= mod;
    (res *= modInv(i)) %= mod;
  }
  return res;
}

int main()
{
  int64 N;
  int K;
  cin >> N >> K;
  int64 mult = 1;
  for(int i = 1; i <= K; i++) {
    (mult *= i) %= mod;
  }
  int64 ret = 0;
  for(int i = 2; i <= K; i++) {
    (mult *= modInv(i)) %= mod;
    if(i & 1) (ret += mod - mult) %= mod;
    else (ret += mult) %= mod;
  }

  cout << modCombination(N, K) * ret % mod << endl;
}

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