111. Minimum Depth of Binary Tree

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if root == None:
            return 0
        left = self.minDepth(root.left)
        right = self.minDepth(root.right)
        depth = 0
        if None in [root.left, root.right]:
            depth = max(left, right) + 1
        else:
            depth = min(left, right) + 1
        return depth