algorithm - Kd-树问题

Question

我正在尝试实施和理解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

你的points拥有x和y价值观。值的中位数x可以通过排序获得x，然后取中间元素的x（对于奇数个）或两个中间元素的points平均值（对于偶数个）。pointsxpoints

或者，使用快速选择算法，例如中位数中位数。