Red/black tree boundary condition settings

The boundary seems to be an algorithm problem, but the data structure has the responsibility to optimize its own structure to simplify the algorithm's judgment on the boundary.

In the red/black tree, a head node (center-left) is generated in the data structure to facilitate the detection of the boundary conditions. The parent pointer of the node is null, and the left and right pointers point to themselves respectively. After a node (root node) is inserted, the pointer is updated, as shown in figure: the head node and the root node use the parent pointer to each other, and both the left and right nodes of the head node point to the root node. This structure helps later traversal and other algorithms to determine the boundary conditions.