给定一个二叉树,找出其最大深度。
二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。
说明: 叶子节点是指没有子节点的节点。
示例:
给定二叉树 [3,9,20,null,null,15,7]
,
3 / \ 9 20 / \ 15 7
返回它的最大深度 3 。
方法一:采用递归的形式,分别求左右子树的最大深度
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
left = right= 0
if root is None:
return 0
else:
left += self.maxDepth(root.left)
right += self.maxDepth(root.right)
result = 1 + max(left, right)
return result
方法二:循环的形式,不断向下做搜索
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if root is None:
return 0
depth = 0
data = [root]
while data:
depth += 1
for i in range(0, len(data)):
if data[0].left:
data.append(data[0].left)
if data[0].right:
data.append(data[0].right)
del data[0]
return depth