NO	Title	Difficulty	Solve Time	Tip
1	Two Sum	Easy	20180201	带标签的break
2	Add Two Numbers	Easy	20180202	LinkNode
3	Longest Substring Without Repeating Characters	Medium	20180202	StringBuilder
4	Median of Two Sorted Arrays	Hard	20180202	逻辑判断，注意中值所在的数组，避免空与越界问题
5	Longest Palindromic Substring	Medium	20180202	求以每个字符为中心的对称，循环s.length()次
6	ZigZag Conversion	Medium	20180205	理解题意，数学公式推导
7	Reverse Integer	Easy	20180205	负数与溢出的处理
8	String to Integer (atoi)	Medium	20180206	atoi，异常处理
9	Palindrome Number	Easy	20180206
10	Regular Expression Matching	Hard	Salving
11	Container With Most Water	Medium	20180208	算法与数学证明
12	Integer to Roman	Medium	20180207	roman numeral
13	Roman to Integer	Easy	20180207	roman numeral
14	Longest Common Prefix	Easy	20180207	最长公共前缀
15	3Sum	Medium	20180209	转化为2Sum，并降低2Sum的时间复杂度
16	3Sum Closest	Medium	20180209	基本同3Sum，注意转化2Sum后，首尾循环时移动点的判断不同
17	Letter Combinations of a Phone Number	Medium	20180209	分治算法
18	4Sum	Medium	20180209	转化为1sum + 3sum
19	Remove Nth Node From End of List	Medium	20180210	链表操作
20	Valid Parentheses	Easy	20180210	栈
21	Merge Two Sorted Lists	Easy	20180210	链表
22	Generate Parentheses	Medium	Salving
23	Merge k Sorted Lists	Easy	Salving
24	Swap Nodes in Pairs	Easy	Salving
25	Reverse Nodes in k-Group	Easy	Salving
26	Remove Duplicates from Sorted Array	Easy	20180326	map/set，注意原数组的修改
27	Remove Element	Easy	20180326	只需要关注不等于val
28	Implement strStr()	Easy	20180327	优化
29	Divide Two Integers	Medium	20180327
30	Substring with Concatenation of All Words	Hard	Salving
31	Next Permutation	Medium	20180327
33	Search in Rotated Sorted Array	Medium	20180727	二分法变形，循环递归
34	Find First and Last Position of Element in Sorted Array	Medium	20180727	二分法变形，循环递归
35	Search Insert Position	Easy	20180730	二分搜索
36	Search Insert Position	Medium	20180731	暴力循环，希望能有更好的解法
37	Search Insert Position	Medium	20180731	暴力循环，希望能有更好的解法
38	Count and Say	Medium	20180817	同斐波那契数列