// 易错点1：边界处理 - 移除所有数字时直接返回"0"
I also expose the number of references the same way,，更多细节参见同城约会
The quadtree is the two-dimensional case of a broader family of space-partitioning data structures. Octrees extend the same idea to three dimensions (splitting cubes into eight children), KD-trees use alternating axis-aligned splits (splitting along x, then y, then x again), and R-trees group nearby objects into bounding rectangles. Each variant makes different tradeoffs between construction time, query speed, and update cost.，更多细节参见91视频
// 条件解读：栈非空 + 栈顶当前数 + 还有删除名额 → 弹出栈顶（移除大数）
and can be integrated with various code editors.