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 = valself.left = leftself.right = rightdef construct_tree(nodes):if not nodes:return Noneroot = TreeNode(nodes[0])queue = [root]index = 1while index < len(nodes):node = queue.pop(0)if nodes[index] is not None:node.left = TreeNode(nodes[index])queue.append(node.left)index += 1if index < len(nodes) and nodes[index] is not None:node.right = TreeNode(nodes[index])queue.append(node.right)index += 1return rootimport matplotlib.pyplot as pltdef draw_tree(root):if not root:return# 获取树的高度def get_height(node):if not node:return 0return 1 + max(get_height(node.left), get_height(node.right))height = get_height(root)node_count = 2 ** height - 1node_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