# 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 not root: return 0
if not root.left and not root.right: return 1
depth = 1
q = [root, None]
minDepth = float(inf)
while q:
node = q.pop(0)
if node is None:
depth += 1
if q: q.append(None)
else:
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
if not node.left and not node.right:
minDepth = min(minDepth, depth)
return minDepth