python 实现树

创建树，遍历树，反转树

thinking：用到的思想都是递归
递归一定要有结束条件

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


class Btree(object):
    def __init__(self, root=None):
        self.root = root

    '''
    build_from
    :param node_list: {'data': 'A', 'left': None, 'right': None, 'is_root': False}
    '''
    @classmethod
    def bulid(cls, list):
        node_dict = {}
        # 制作节点
        for item in list:
            data = item['data']
            node_dict[data] = Bnode(data)
        # 把节点组装成数
        for item in list:
            data = item['data']
            node = node_dict[data]
            if node['is_root']:
                root = node
            node.left = node_dict.get(item['left'])
            node.right = node_dict.get(item['right'])
        return cls(root)

    def preorder(self, subtree):
        # 先序
        if subtree is not None:
            print(subtree.data)
            self.preorder(subtree.left)
            self.preorder(subtree.right)

    '''反转'''

    def reverse(self, subtree):
        if subtree is not None:
            subtree.left, subtree.right = subtree.right, subtree.left
            self.reverse(self, subtree.left)
            self.reverse(self, subtree.right)