Kd-Tree问题

Question

我正在尝试实施并理解KdTree，以下是我找到的链接。 http://ldots.org/kdtree/#buildingAkDTree 但我无法理解以下算法

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)

我不明白是什么意思 Calculate the median x-value.

Answer 1

您的points有x和y个值。可以通过x排序，然后获取中间元素的x（针对奇数x）或平均值来获取median points个值两个中间points'x（偶数points）。

或者，使用快速selection algorithm，例如中位数中位数。