. Preface
Binary tree: refers to a tree with only two child nodes and a total of three nodes: the root node, the left child node, and the right child node.
According to the traversal order of the three nodes, it is divided into three types: preorder, middle order and postorder traversal.
Note: The root node modified by the previous location word (I think I can remember this by knowing this)
Preorder:
Root node -> Left child node -> Right child node: A->B->C
Middle order:
left child node -> root node -> right child node: B->A->C
Post sequence:
left child node -> right child node -> root node: B->C->A
When the child node encountered is not a leaf node, the above steps are nested to read.
The more important of the three traversals is the in-order traversal, because many sorts (such as heap sort) are used. (I will find time to write about the realization of the three traversals)