与你交谈系列#3

from typing import anyclass treenode:    def __init__(self, data: any):        self.data = data        self.left = none        self.right = none# define all the nodes we needroot = treenode('r')nodea = treenode('a')nodeb = treenode('b')nodec = treenode('c')noded = treenode('d')# connect all the nodes between each otherroot.left = nodearoot.right = nodebnodea.left = nodecnodea.right = noded# what we've got    r   /   a   b /  c   d

"""preorder - is done by visiting the root node first, then recursively do a pre-order traversal of the left subtree, followed by a recursive pre-order traversal of the right subtree.this traversal is "pre" order because the node is visited "before" the recursive pre-order traversal of the left and right subtrees."""def pre_order(node):    if node:        print(node.value)        pre_order(node.left)        pre_order(node.right)

"""postorder - works by recursively doing a post-order traversal of the left subtree and the right subtree, followed by a visit to the root node.what makes this traversal "post" is that visiting a node is done "after" the left and right child nodes are called recursively."""def post_order(node):    if node:        post_order(node.left)        post_order(node.right)        print(node.value)

"""inOrder - does a recursive In-order Traversal of the left subtree, visits the root node, and finally, does a recursive In-order Traversal of the right subtree.What makes this traversal "in" order, is that the node is visited in between the recursive function calls. The node is visited after the In-order Traversal of the left subtree, and before the In-order Traversal of the right subtree."""def in_order(node):    if node:        in_order(node.left)        print(node.value)        in_order(node.right)