[Leetcode][python]Minimum Depth of Binary Tree

class 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.left)+1
        if root.left == None and root.right != None:
            return self.minDepth(root.right)+1
        return min(self.minDepth(root.left),self.minDepth(root.right))+1