104. 二叉树的最大深度
思路:
递归实现:
# 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
else:
return max(self.maxDepth(root.left) +1, self.maxDepth(root.right) +1)
第二种方法:广度优先搜索
一层层的遍历
# 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):
if root is None:
return 0
paths = [root]
count = 0
line = [] # 保存下一层的结点
while paths:
node = paths.pop()
if node.left:
line.append(node.left)
if node.right:
line.append(node.right)
if len(paths) == 0: 当一层遍历完之后,将下一层的结点更新到paths中
paths = line
count += 1
line = []
return count