从InOrder字符串表示构建BinaryTree

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

def buildTree(inorder):
    def buildTreeHelper(inorder, start, end):
        if start > end:
            return None
        
        mid = (start + end) // 2
        root = TreeNode(inorder[mid])
        
        root.left = buildTreeHelper(inorder, start, mid - 1)
        root.right = buildTreeHelper(inorder, mid + 1, end)
        
        return root
    
    return buildTreeHelper(inorder, 0, len(inorder) - 1)

# 示例用法
inorder = [2, 5, 7, 10, 12, 15, 20]
root = buildTree(inorder)