基于Python字典构建二叉树：树形打印异常问题求助

问题原因 #

1. 节点创建逻辑错误：原代码中，若节点不在data字典里（比如Akon、Frank这类无下属的员工），直接返回None，导致这些节点根本没被实例化为TreeNode对象。实际上这类节点是叶子节点，应当被创建，只是没有子节点。
2. 空值处理逻辑无问题，但被节点创建错误掩盖：原代码对子节点为None的情况已有判断，但核心问题是叶子节点未被创建，导致打印时缺失层级。

修复方案 #

修改construct_binary_tree函数：

• 优先创建当前节点，无论它是否在data中（不在则为叶子节点）
• 仅当节点存在于data中时，才处理其下属子节点
• 子节点为None时跳过创建

修复后的完整代码 #

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

def construct_binary_tree(data, root_key):
    # 空值直接返回None，不创建节点
    if root_key is None:
        return None
    # 先创建当前节点，无论是否有下属
    print("Constructing node:", root_key)
    root = TreeNode(root_key)
    
    # 仅当节点在data中时，处理子节点
    if root_key in data:
        children = data[root_key]
        left_child_key = children[0] if len(children) > 0 else None
        right_child_key = children[1] if len(children) > 1 else None
        print("Left child of", root_key, ":", left_child_key)
        print("Right child of", root_key, ":", right_child_key)
        
        root.left = construct_binary_tree(data, left_child_key)
        root.right = construct_binary_tree(data, right_child_key)
    
    return root

def print_tree(root, depth=0):
    if root:
        print("   " * depth + f"|-- {root.key}")
        print_tree(root.left, depth + 1)
        print_tree(root.right, depth + 1)

# 完整的经理-员工数据
data = {
    "Amy": ["Alice", "Charlie"],
    "Alice": ["Akon", "Eve"],
    "Eve": ["Frank", None],
    "Charlie": ["Bob", "Grace"]
}

# 构建二叉树
root_key = next(iter(data))
root = construct_binary_tree(data, root_key)

# 打印树形结构
print("\n树形结构输出：")
print_tree(root)

运行结果 #

Constructing node: Amy
Left child of Amy : Alice
Right child of Amy : Charlie
Constructing node: Alice
Left child of Alice : Akon
Right child of Alice : Eve
Constructing node: Akon
Constructing node: Eve
Left child of Eve : Frank
Right child of Eve : None
Constructing node: Frank
Constructing node: Charlie
Left child of Charlie : Bob
Right child of Charlie : Grace
Constructing node: Bob
Constructing node: Grace

树形结构输出：
|-- Amy
   |-- Alice
      |-- Akon
      |-- Eve
         |-- Frank
   |-- Charlie
      |-- Bob
      |-- Grace

内容的提问来源于stack exchange，提问作者user2657189