Given an array of integers, every element appears twice except for one. Find that single one.
Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
一个整型数组，除一个元素外，其余的元素都出现两次，要求不用额外内存，线性时间内找到这个元素
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
For example, “A man, a plan, a canal: Panama” is a palindrome. “race a car” is not a palindrome.
Note: Have you consider that the string might be empty? This is a good question to ask during an interview.
For the purpose of this problem, we define empty string as valid palindrome.
即判断一个字符串的字符部分是不是回环字符串。即出去非字母，数字以外的字符，剩下的部分满足正反相同。
Say you have an array for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
上一个问题的变形，即求累计利润的最大值。就是按顺序相减的和。
Say you have an array for which the ith element is the price of a given stock on day i.
If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.
Example 1:
Input: [7, 1, 5, 3, 6, 4]
Output: 5
max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
Example 2:
Input: [7, 6, 4, 3, 1]
Output: 0
In this case, no transaction is done, i.e. max profit = 0.
即给定一个数组，按从前往后顺序计算，求最大差。
部署Anaconda 科学计算包，并通过
conda install -c conda-forge tensorflow
部署tensorflow相关包。在ipython环境下执行下列命令下载训练数据包
from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)
结果报错,
[Errno 104] Connection reset by peer
Given an index k, return the kth row of the Pascal’s triangle.
For example, given k = 3, Return [1,3,3,1].
Note: Could you optimize your algorithm to use only O(k) extra space?
即直接返回杨辉三角形的某一行元素，额外要求是只让使用O（k）的空间
学习TensorFlow过程中读的一篇文章，索性就翻译出来，虽然收获感觉不是很大。
原文地址：How TensorFlow Works
Given numRows, generate the first numRows of Pascal’s triangle.
For example, given numRows = 5, Return
[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]
没记错的话，这个应该叫杨辉三角型。很简单的题
Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.
For example: Given the below binary tree and sum = 22,
5
/ \
4 8
/ / \
11 13 4
/ \ / \
7 2 5 1
return
[
[5,4,11,2],
[5,8,4,5]
]
即Path Sum问题的进一步，不仅仅是判断是否存在路径，而是找出所有的路径。
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
For example: Given the below binary tree and sum = 22,
5
/ \
4 8
/ / \
11 13 4
/ \ \
7 2 1
return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None