python 树

class Node:
    """
    节点类
    """
    def __init__(self, value=None, left=None, right=None):
        self.val = value
        self.left = left
        self.right = right

class Tree:
    """
    树类
    """
    def __init__(self):
        self.root = Node()
        self.queue = []

    def add(self, val):
        """
        为树添加节点
        """
        node = Node(value=val)

        if self.root.val is None:  # 如果树是空的，则当前节点为根节点
            self.root = node
            self.queue.append(self.root)
        else:
            treeNode = self.queue[0]
            if treeNode.left is None:
                treeNode.left = node
                self.queue.append(treeNode.left)
            else:
                treeNode.right = node
                self.queue.append(treeNode.right)
                self.queue.pop(0)  # 如果该节点存在左右子树，将此节点丢弃

    def pre_order(self,node):       # 先序遍历：根左右
        print(node.val)
        if node.left is not None:
            self.pre_order(node.left)
        if node.right is not None:
            self.pre_order(node.right)
            
    def center_order(self,node): # 中序遍历：左根右
        if node.left is not None:
            self.center_order(node.left)
        print(node.val)
        if node.right is not None:
            self.center_order(node.right)
    
    def post_order(self,node): # 后序遍历：左右根
        if node.left is not None:
            self.post_order(node.left)
        if node.right is not None:
            self.post_order(node.right)
        print(node.val)


if __name__ == '__main__':
    tree = Tree()  # 新建一个树对象
    for val in range(10):
        tree.add(val)

    tree.post_order(tree.root)