• 不断判断随机数的大小，如果它能大于某个值维持一段时间，输出时间，否则重新计时。

int main()
{
    int num = 0;
    int count = 0;
    std::chrono::steady_clock::time_point  start, end;
    double duration;

    while(1)
    {
        std::srand(time(0));
        count = rand() % 1000000;
        if(count > 680000)
        {
            if(num==0)
                start = std::chrono::steady_clock::now();

            num++;
            end = std::chrono::steady_clock::now();
            duration = std::chrono::duration<double>(end - start).count();
            cout << "count: " << count << endl;
            cout << "time elapsed " << static_cast<int>(duration) << endl;
        }
        else
        {
            duration = 0;
            num = 0;
            cout << endl;
        }
    }
    return 0;
}

• 判断一个点是否在多边形中

opencv函数: double pointPolygonTest(InputArray contour, Point2f pt, bool measureDist)

当measureDist设置为true时，返回实际距离值。若返回值为正，表示点在多边形内部，返回值为负，表示在多边形外部，返回值为0，表示在多边形上。
当measureDist设置为false时，返回 -1、0、1三个固定值。若返回值为+1，表示点在多边形内部，返回值为-1，表示在多边形外部，返回值为0，表示在多边形上。

• 计算点到直线的距离

/*
 * @tparam T point type
 * @param first Given the starting point of a line segment
 * @param last The endpoint of a given line segment
 * @param third Given point
 * @return T Distance from point to line
 */
template <typename T>
static T PointToLineDistance(const Point<T>& first, const Point<T>& last, const Point<T>& third) {
    float dis_suqare =
        ((first.y - last.y) * third.x + (last.x - first.x) * third.y +
         (first.x * last.y - last.x * first.y)) *
        ((first.y - last.y) * third.x + (last.x - first.x) * third.y +
         (first.x * last.y - last.x * first.y)) /
        ((last.x - first.x) * (last.x - first.x) + (last.y - first.y) * (last.y - first.y));
    return std::sqrt(dis_suqare);
}

• 求图形的外接圆

OpenCV绘制最小外接矩形、最小外接圆
pointPolygonTest函数