45.前中后序遍历

#coding:utf-8
#二叉树的遍历
#简单的二叉树节点类
class Node(object):
    def __init__(self,value,left,right):
        self.value = value
        self.left = left
        self.right = right

#中序遍历:遍历左子树,访问当前节点,遍历右子树

def mid_travelsal(root):
    if root.left is None:
        mid_travelsal(root.left)
    #访问当前节点
    print(root.value)
    if root.right is not None:
        mid_travelsal(root.right)

#前序遍历:访问当前节点,遍历左子树,遍历右子树

def pre_travelsal(root):
    print (root.value)
    if root.left is not None:
        pre_travelsal(root.left)
    if root.right is not None:
        pre_travelsal(root.right)

#后续遍历:遍历左子树,遍历右子树,访问当前节点

def post_trvelsal(root):
    if root.left is not None:
        post_trvelsal(root.left)
    if root.right is not None:
        post_trvelsal(root.right)
    print (root.value)