leetcode104-- Maximum Depth of Binary Tree (求二叉树的深度)

# 小郑之家~

### 先用递归的办法，比较容易

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
def maxDepth(self, root: TreeNode) -> int:
if not root:
return 0
return max(self.maxDepth(root.left), self.maxDepth(root.right))+1

### 非递归的解法, 层次遍历(利用队列来实现)

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
def maxDepth(self, root: TreeNode) -> int:

if not root:
return 0
queue = []   # 申请一个队列
queue.append(root）
level = 0   # 结果初始化
while len(queue) >0:   # 当队列不空的时候
cur_len = len(queue)   # 得到当前层的长度
level += 1          # 深度加1
while cur_len:  # 只要当前这一层的没有用完的时候，就把第一个给弹出来, 同时要看看它有没有左右子树，有的话就放入队列中去.
front = queue.pop(0)
if front.left:
queue.append(front.left)
if front.right:
queue.append(front.right)
cur_len -= 1

return level