순열

void swap(int &a, int &b)
{
    int temp = a;
    a = b;
    b = temp;
}

void permutation(vector<int> &v, int depth, int n, int r)
{
    if (depth == r)
    {
        for(int i = 0; i < r; i++)
            cout << v[i] << " ";
        cout << endl;
        return;
    }
    
    for(int i = depth; i < n; i++)
    {
        swap(v[depth], v[i]);
        permutation(v, depth + 1, n, r);
        swap(v[depth], v[i]);
    }
}