# Definition for a binary tree node.# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    def minDepth(self, root: TreeNode) -> int:        if root is None:            return 0        if root.left and root.right:            return min(self.minDepth(root.left), self.minDepth(root.right)) + 1        #   3        #  / \        # 9        # 返回的应该是2，而不是1        else:            return max(self.minDepth(root.left), self.minDepth(root.right)) + 1