我有一个大二维的网格,让我们说 10000 X 10000 。 我需要从这些网格中选择 1000 个随机点, 但我也需要注意这两个点中没有一个是相同的。 我脑中的标准方式是在选择每个点后都检查所有先前的条目, 看看是否已经选中了该点, 但对于大网格和大量点来说,这将会变得无效。 是否有更好的方法来做到这一点? 我正在使用 C/ p > < / div > 。
随机选择任何点然后丢弃它, 如果它存在于 < em> 选中点 < / 选择点 > 列表中, 则不应无效, 只要您已经对 < em > 选中点 < / 选择点 > 的收藏进行了精密排序, 并且也可以轻松插入 。
另外,根据如何定义您的点(即它们是否都与您定义的类别或曲线相关联),您可以在点对象上添加一个布尔变量,名为 Sselective 。一旦您选择了一个点,请检查它是否被标记为 Sselective 。如果不是,请将其添加到列表中,并将 Sselective 值修改为 TRUE 。否则,继续选择随机点。
这对大网格和大量点数看来是无效率的。
不一定,效率低下有两个潜在原因:
O(1) time. For this, std::unordered_set would be a good candidate. The size of the set will grow linearly in the number of elements you need to select, and will be completely independent of the grid size.您可以实施这样的算法 :
- Create an empty mapping from hashes to points
- select random point
- calculate hash
- if hash in mapping, goto 1
- save hash & point
- if not enough points yet, goto 1
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