"""
二叉树的构建与遍历
"""


class TreeNode:
 """
 二叉树节点
 """

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


class TwoTree:
 """
 二叉树
 """

 def __init__(self, root=None):
 self.root = root

 def is_empty(self):
 if self.root is None:
 return True
 else:
 return False

 def pre_order(self, node):
 """
 前序遍历
 :param node:
 :return:
 """
 if node is None:
 return
 print(node.data, end=' ')
 self.pre_order(node.left)
 self.pre_order(node.right)

 def in_order(self, node):
 """
 中序遍历
 :param node:
 :return:
 """
 if node is None:
 return
 self.in_order(node.left)
 print(node.data, end=' ')
 self.in_order(node.right)

 def post_order(self, node):
 """
 后序遍历
 :param node:
 :return:
 """
 if node is None:
 return
 self.post_order(node.left)
 self.post_order(node.right)
 print(node.data, end=' ')


if __name__ == "__main__":
 # 按照后序遍历增加节点
 b = TreeNode('B')
 f = TreeNode('F')
 g = TreeNode('G')
 d = TreeNode('D', f, g)
 i = TreeNode('I')
 h = TreeNode('H')
 e = TreeNode('E', i, h)
 c = TreeNode('C', d, e)
 a = TreeNode('A', b, c)

 # 初始化树对象,传入根节点
 bt = TwoTree(a)
 print("前序遍历")
 bt.pre_order(bt.root)
 print("\n中序遍历")
 bt.in_order(bt.root)
 print("\n后序遍历")
 bt.post_order(bt.root)