（树）-线索二叉树

class Node:
    def __init__(self):
        self.data = 0
        self.right = None
        self.left = None
        self.left_thread = 0  # 0没有子节点，1有子节点
        self.right_thread = 0


def add(root, val):
    newnode = Node()
    newnode.data = val
    pre = newnode
    if root == None:
        root = newnode
        root.left = root
        root.right = None
        root.left_thread = 0
        root.right_thread = 1
        return root
    current = root.right
    if current == None:
        root.right = newnode
        newnode.left = root
        newnode.right = root
        return root
    parent = root
    pos = 0
    while current != None:
        if current.data > val:
            if pos != -1:
                pos = -1
                pre = parent
            parent = current
            if current.left_thread == 1:
                current = current.left
            else:
                current = None
        else:
            if pos != 1:
                pos = 1
                pre = parent
            parent = current
            if current.right_thread == 1:
                current = current.right
            else:
                current = None
    if parent.data > val:
        parent.left = newnode
        parent.left_thread = 1
        newnode.left = pre
        newnode.right = parent
    else:
        parent.right = newnode
        parent.right_thread = 1
        newnode.left = parent
        newnode.right = pre
    return root


def trace(root):
    '''
    遍历线索二叉树
    :param root:
    :return:
    '''
    t = root
    while True:
        if t.right_thread == 0:
            # 右线索访问中节点
            t = t.right
        else:
            t = t.right
            while t.left_thread != 0:
                t = t.left
        if t != root:
            print('[%d]' % t.data, end=' ')
        if t == root:
            break


data = [1, 7, 3, 4, 5, 2, 9, 11, 13, 15, 12]

root = None
for i in range(len(data)):
    root = add(root, data[i])
trace(root)

output:

[2] [3] [4] [5] [7] [9] [11] [12] [13] [15]