写了一个二叉树构造函数和画图函数，方便debug

代码 

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


def construct_tree(nodes):
    if not nodes:
        return None

    root = TreeNode(nodes[0])
    queue = [root]
    index = 1

    while index < len(nodes):
        node = queue.pop(0)

        if nodes[index] is not None:
            node.left = TreeNode(nodes[index])
            queue.append(node.left)
        index += 1

        if index < len(nodes) and nodes[index] is not None:
            node.right = TreeNode(nodes[index])
            queue.append(node.right)
        index += 1

    return root



import matplotlib.pyplot as plt

def draw_tree(root):
    if not root:
        return

    # 获取树的高度
    def get_height(node):
        if not node:
            return 0
        return 1 + max(get_height(node.left), get_height(node.right))

    height = get_height(root)
    node_count = 2 ** height - 1
    node_positions = {}

    # 使用层序遍历确定每个节点的位置
    queue = deque([(root, 0, 0)])  # (节点, 层级, 水平位置)
    while queue:
        node, level, x = queue.popleft()
        y = height - level - 1  # 从底部开始绘制
        node_positions[node] = (x, y)

        if node.left:
            queue.append((node.left, level + 1, x - 2 ** (height - level - 2)))
        if node.right:
            queue.append((node.right, level + 1, x + 2 ** (height - level - 2)))

    # 绘制节点和连接线
    fig, ax = plt.subplots(figsize=(10, 10))
    ax.set_xlim(-node_count, node_count)
    ax.set_ylim(-1, height)
    ax.axis('off')

    for node, (x, y) in node_positions.items():
        # 绘制节点
        ax.text(x, y, str(node.val), ha='center', va='center',
                bbox=dict(facecolor='white', edgecolor='black', boxstyle='circle'))

        # 绘制连接线
        if node.left and node.left in node_positions:
            x1, y1 = node_positions[node.left]
            ax.plot([x, x1], [y, y1], 'black')
        if node.right and node.right in node_positions:
            x1, y1 = node_positions[node.right]
            ax.plot([x, x1], [y, y1], 'black')

    plt.show()

# 按装订区域中的绿色按钮以运行脚本。
if __name__ == '__main__':
    print_hi('PyCharm')
    solution = Solution()
    nodes = [3,9,20,None,None,15,7,8,6,8,5,4,6,1,2]
    root = construct_tree(nodes)
    draw_tree(root)

效果