实现二叉树的先序、中序、后序遍历，包括递归方式和非递归方式

class TreeNode:
    
    def __init__(self,x):
        self.value = x
        self.right = None
        self.left = None
        
def createTree(root):
    
    data = input("input data")
    if data == "#"
        root = None
    else:
        root = TreeNode(element)
        root.left = createTree(root.left)
        root.right = createTree(root.right)
    
    return  root

"""
    前序遍历
"""
def preOrderRecur(head):
    
    if head == None:
        return 
    print(head.value + ' ')
    preOrderRecur(head.left)
    preOrderRecur(head.right)
    
"""
    中序遍历
"""
def inOrderRecur(head):
    
    if head == None:
        return
    inOrderRecur(head.left)
    print(head.value + ' ' )
    inOrderRecur(head.right)
    
"""
    后序遍历
"""
def posOrderRecur(head):
    
    if head == None:
        return
    posOrderRecur(head.left)
    posOrderRecur(head.right)
    print(head.value + ' ')


"""
    非递归方式
"""
 
def preOrderUnRecur(head):
    print("pre-order:")
    if head!=None:
        stack = []
        stack.append(head)
        while len(stack)!=0:
            head = stack.pop()
            print(head.value + " ")
            if head.right!=None:
                stack.push(head.right)
            if head.left!=None:
                stack.push(head.left)
    print(" ")
    
    
def inOrderUnRecur(head):
    """
    先把所有左子树全都压入栈中
    """
    print("in-order:")
    if head!=None:
        stack = []
        while len(stack)!=0 or head!=None:
            if head!= None:
                stack.push(head)
                head = head.left
            else:
                head = stack.pop()
                print(head.value + " ")
                head = head.right
                
    print(" ")
    
def posOrderUnRecur(head):
    
    print("pos-order:")
    if head!=None:
        s1 = []
        s2 = []
        s1.push(head)
        while len(s1)!=0:
            head = s1.pop()
            s2.push(head)
            
            if head.left!=None:
                s1.push(head.left)
            if head.right!=None:
                s1.push(head.right)
                
        while s2.isEmpty() is not True:
            print(s2.pop().value + " ")
            
    print(" ")