二叉樹(shù)的遍歷分為深度優(yōu)先遍歷（Depth First Traversal）和廣度優(yōu)先遍歷（Breath First Traversal also called Levelorder Traversal）。其中深度優(yōu)先遍歷又分為先序遍歷（Preorder Traversal），中序遍歷（Inorder Traversal）和后續(xù)遍歷（Postorder Traversal）。
Pre-order Traversal
Visit the root, traverse the left subtree, traverse the right subtree.
- recursive
- stack
In-order Traversal
Traverse the left subtree, visit the root, traverse the right subtree.
- recursive
- stack
Post-order Traversal
Traverse the left subtree, traverse the right subtree, visit the root.
- recursive
- stack
