初始化一个数据元素为字符串类型的二叉树，并对其实现创建及先序、中序、后序三种遍历

以下是 Python 代码实现：

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

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

    def insert(self, data):
        node = Node(data)
        if self.root is None:
            self.root = node
        else:
            queue = []
            queue.append(self.root)
            while queue:
                curr = queue.pop(0)
                if curr.left is None:
                    curr.left = node
                    break
                elif curr.right is None:
                    curr.right = node
                    break
                else:
                    queue.append(curr.left)
                    queue.append(curr.right)

    def preorder(self, node):
        if node is not None:
            print(node.data, end=' ')
            self.preorder(node.left)
            self.preorder(node.right)

    def inorder(self, node):
        if node is not None:
            self.inorder(node.left)
            print(node.data, end=' ')
            self.inorder(node.right)

    def postorder(self, node):
        if node is not None:
            self.postorder(node.left)
            self.postorder(node.right)
            print(node.data, end=' ')

# 创建二叉树
bt = BinaryTree()
bt.insert('A')
bt.insert('B')
bt.insert('C')
bt.insert('D')
bt.insert('E')
bt.insert('F')
bt.insert('G')

# 先序遍历
print('先序遍历：')
bt.preorder(bt.root)
print()

# 中序遍历
print('中序遍历：')
bt.inorder(bt.root)
print()

# 后序遍历
print('后序遍历：')
bt.postorder(bt.root)
print()

输出结果：

先序遍历：
A B D E C F G 
中序遍历：
D B E A F C G 
后序遍历：
D E B F G C A