求排列数

#include <iostream>
using namespace std;
typedef long long ll;
ll permutation(ll n, ll k)
{
    if(0 == k)
    {
        return 1;
    }
    return permutation(n, k - 1) * (n - k + 1);
}
int main()
{
    cout << permutation(10, 3) << endl;
    return 0;
}

720