algorithm - Kd树问题

Question

我正在尝试实现和理解 KdTree，以下是我找到的链接。 http://ldots.org/kdtree/#buildingAkDTree 但是我不明白下面的算法

tuple function build_kd_tree(int depth, set points):
    if points contains only one point:
        return that point as a leaf.

    if depth is even:
        Calculate the median x-value.
        Create a set of points (pointsLeft) that have x-values less than
            the median.
        Create a set of points (pointsRight) that have x-values greater
            than or equal to the median.
    else:
        Calculate the median y-value.
        Create a set of points (pointsLeft) that have y-values less than
            the median.
        Create a set of points (pointsRight) that have y-values greater
            than or equal to the median.

    treeLeft = build_kd_tree(depth + 1, pointsLeft)
    treeRight = build_kd_tree(depth + 1, pointsRight)

    return(median, treeLeft, treeRight)

我不明白什么意思 计算 x 值的中位数。

Answer 1

您的点有x和y值。 median x 值可以通过按 x 排序获得，然后取中间元素的 x (对于奇数个 points) 或两个中间 points' x 的平均值(对于偶数个 points)。

或者，使用快速 selection algorithm例如中位数。