二叉树前序、中序、后序遍历，递归和非递归实现

class TreeNode:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None

class Order:
    def __init__(self):
        self.result = []

    def preOrder(self, node):
        if not node:
            return
        self.result.append(node.data)
        self.preOrder(node.left)
        self.preOrder(node.right)

    def preOrder2(self, node):
        nodeList = []
        while nodeList or node:
            if node:
                self.result.append(node.data)
                nodeList.append(node)
                node = node.left
            else:
                node = nodeList.pop()
                node = node.right

    def midOrder(self, node):
        if not node:
            return
        self.midOrder(node.left)
        self.result.append(node.data)
        self.midOrder(node.right)

    def midOrder2(self, node):
        nodeList = []
        while nodeList or node:
            if node:
                nodeList.append(node)
                node = node.left
            else:
                node = nodeList.pop()
                self.result.append(node.data)
                node = node.right

    def posOrder(self, node):
        if not node:
            return
        self.posOrder(node.left)
        self.posOrder(node.right)
        self.result.append(node.data)

    def posOrder2(self, node):
        nodeList = []
        while nodeList or node:
            if node:
                nodeList.append(node)
                node = node.left
            else:
                node = nodeList[-1]
                if not node.right:
                    self.result.append(node.data)
                    nodePop = nodeList.pop()
                    nodeNow = nodeList[-1]
                    # 出栈的是左子树节点，跳到右子树
                    if nodeNow.left == nodePop:
                        node = nodeNow.right
                    # 出栈的是右子树节点时，双亲节点出栈
                    elif nodeNow.right == nodePop:
                        self.result.append(nodeNow.data)
                        nodeList.pop()
                        if nodeList:
                            node = nodeList[-1].right
                        else:
                            node = None
                else:
                    node = node.right
                    nodeList.append(node)

if __name__ == '__main__':
    A = TreeNode(1)
    B = TreeNode(2)
    C = TreeNode(3)
    D = TreeNode(4)
    E = TreeNode(5)
    F = TreeNode(6)
    A.left = B
    A.right = C
    B.left = D
    B.right = E
    C.left = F
    ss = Order()
    ss.posOrder(A)
    print(ss.result)