complexity of recursive string permutation function

Question

From: Are there any better methods to do permutation of string?

what is the complexity of this function???

void permute(string elems, int mid, int en         


        

Answer 1

long long O(int n)
{
    if (n == 0)
        return 1;
    else 
       return 2 + n * O(n-1);
}

int main()
{
    //do something
    O(end - mid);
}

This will calculate complexity of the algorithm.

Actualy O(N) is N!!! = 1 * 3 * 6 * ... * 3N