.编写程序实现二叉树的建树、先序递归遍历、中序递归遍历、后序递归遍历4个基本操作;(必须完成)

好的，以下是二叉树的建树、先序递归遍历、中序递归遍历、后序递归遍历这四个基本操作的程序实现：

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

class BinaryTree:
    def __init__(self):
        self.root = None

    def build_tree(self, nodes):
        queue = [None] * len(nodes)
        for i in range(len(nodes)):
            if nodes[i] is not None:
                node = TreeNode(nodes[i])
                if i == 0:
                    self.root = node
                else:
                    parent_index = (i - 1) // 2
                    if i % 2:
                        queue[parent_index].left = node
                    else:
                        queue[parent_index].right = node
                queue[i] = node

    def preorder_traversal(self, node):
        if node is None:
            return
        print(node.val)
        self.preorder_traversal(node.left)
        self.preorder_traversal(node.right)

    def inorder_traversal(self, node):
        if node is None:
            return
        self.inorder_traversal(node.left)
        print(node.val)
        self.inorder_traversal(node.right)

    def postorder_traversal(self, node):
        if node is None:
            return
        self.postorder_traversal(node.left)
        self.postorder_traversal(node.right)
        print(node.val)

例如，如果我们要创建如下的二叉树：

      1
     / \
    2   3
   / \
  4   5

可以这样调用上述程序：

tree = BinaryTree()
tree.build_tree([1, 2, 3, 4, 5])
tree.preorder_traversal(tree.root)
tree.inorder_traversal(tree.root)
tree.postorder_traversal(tree.root)

输出结果如下：

1
2
4
5
3
4
2
5
1