# 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  not root:            return 0        queue=[root]        res=[]        depth=0        while queue:            depth=depth+1            l=len(queue)            for i in range(l):                t=queue.pop(0)                if not t.left and not t.right:                    return depth                if t.left:                    queue.append(t.left)                if t.right:                    queue.append(t.right)