P3414 SAC#1 - 组合数

组合数的性质，求(1<<(n-1))%mod即可。其实要快速幂。

#include<bits/stdc++.h>
#define MOD 6662333
using namespace std;
unsigned long long n;

unsigned long long p(unsigned long long x)
{
    unsigned long long t=2;
    while(x%2==0)
    {
        t*=t;
        t%=MOD;
        x>>=1;
    }
    unsigned long long result=1;
    while(x>0)
    {
        if(x%2==1)
        {
            result*=t;
            result%=MOD;
        }
        x>>=1;
        t*=t;
        t%=MOD;
    }
    return result%MOD;
}

int main()
{
  cin>>n;
  n--;
  cout<<p(n);
return 0;
}