Leikou 111 minimum depth of binary tree

# 层次遍历
class Solution:
    def minDepth(self, root: TreeNode) -> int:

        if root is None:
            return 0
        
        queue = []
        layer = []
        cur = root
        queue.append(cur)
        layer.append(1)
        min_layer = 1
        cur_layer = 1
        while queue:
            cur = queue.pop(0)
            cur_layer = layer.pop(0)
            print(cur.val)
            if cur.left is None and cur.right is None:
                min_layer = cur_layer
                # print('min_layer',min_layer)
                break
                
            if cur.left:
                queue.append(cur.left)
                layer.append(cur_layer+1)
            if cur.right:
                queue.append(cur.right)
                layer.append(cur_layer+1)
        
        return min_layer

# 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
# 前序遍历
class Solution:
    def minDepth(self, root: TreeNode) -> int:
        if root is None:
            return 0 
        # 前序遍历
        self.min_dep = 0
        def PreOrder(root,layer):
            print(root.val)
            if root.left is None and root.right is None:
                if self.min_dep == 0:
                    self.min_dep = layer
                elif self.min_dep>layer:
                    self.min_dep=layer
            if root.left:
                PreOrder(root.left, layer+1)
            if root.right:
                PreOrder(root.right, layer+1)
        PreOrder(root,1)
            
        return self.min_dep