# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution(object):    def minDepth(self, root):        """        :type root: TreeNode        :rtype: int        """        if root == None:            return 0        if root.left == None and root.right != None:            return self.minDepth(root.right)+1        if root.left != None and root.right == None:            return self.minDepth(root.left)+1        return min(self.minDepth(root.right),self.minDepth(root.left))+1