Binary sort tree

** Definition ：** Left subtree node value < Root value < Right subtree node value , By default, the same keywords of two nodes are not allowed
** Search operation ：** Start at the root node , If the target value is smaller, look to the left , If the target value is larger, look to the right
** The insert ：** Find where to insert （ It must be a leaf node ）, Be sure to change its parent node pointer
** Delete operation ：**① The deleted node is a leaf , Delete directly ;② The deleted node has only left or right subtrees , Replace its position with its subtree ③ The deleted node has left 、 Right subtree ： It can be replaced by its successor nodes , Then delete the successor node or replace it with its predecessor node , Delete the precursor node precursor ;
Forerunner ： The lowest right node in the left subtree
The subsequent ： The lowest left node in the right subtree

Search efficiency analysis ：
Depends on the height of the tree , best O ( log n ), The worst O ( n )