c – 减少找到N线交叉点所需的时间

这是我的代码：

using namespace std;

typedef struct Point
{
     long long int x;
     long long int y;
} ;


bool fun(Point p0,Point p1,Point p2,Point p3)
{
    double s1_x,s1_y,s2_x,s2_y;
    s1_x = p1.x - p0.x;     s1_y = p1.y - p0.y;
    s2_x = p3.x - p2.x;     s2_y = p3.y - p2.y;

    double s,t;
    s = (-s1_y * (p0.x - p2.x) + s1_x * (p0.y - p2.y)) / (-s2_x * s1_y + s1_x * s2_y);
    t = ( s2_x * (p0.y - p2.y) - s2_y * (p0.x - p2.x)) / (-s2_x * s1_y + s1_x * s2_y);

    if (s >= 0 && s <= 1 && t >= 0 && t <= 1)
    {
        return 1; // Collision detected
    }

    return 0; // No collision
}


int main()
{
     long long int n // number of line segments;

     Point p[n],q[n]; // to store end points of line segments

    for( long long int i=0;i<n;i++)
    {

// line segments is defined by 2 points P(x1,y1) and Q(x2,y2)
        p[i].x=x1;
        p[i].y=y1;
        q[i].x=x2;
        q[i].y=y2;
    }

    for( long long int i=0;i<n-1;i++)
    {
        for( long long int j=i+1;j<n;j++)
        {
            if(fun(p[i],q[i],p[j],q[j]))
               count++;
        }

    }

    return 0;
}

有人可以帮我减少这个程序的时间复杂度吗？