leetcode 104_MaximumDepthOfBinaryTree_easy.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

__author__ = 'circlezhou'

'''
Description:
Given a binary tree, find its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
'''

'''
Solution: using DFS
'''

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

class Solution:
def maxDepth(self, root):
"""
:type root: TreeNode
:rytype int
"""
if root == None:
return 0
i = 1
res = []
def dfs(root, res, i):
if root == None:
return
if len(res) < i:
res.append(i)
dfs(root.left, res, i+1)
dfs(root.right, res, i+1)
dfs(root, res, i)
return res[-1]

'''
Solution: BFS
'''
class Solution:
def maxDepth(self, root):
if root == None:
return 0
queue = []
layers = 0
queue.append(root)
while(len(queue) != 0):
tmp = []
while(len(queue) != 0):
head = queue.pop(0)
if head.left != None:
tmp.append(head.left)
if head.right != None:
tmp.append(head.right)
queue = tmp
layers += 1
return layers

'''
Better Solution: one line
'''
class Solution(object):
def maxDepth(self, root):
return 1 + max(map(self.maxDepth, (root.left, root.right))) if root else 0