ID	Title	Difficulty
3	Longest Substring Without Repeating Characters	Medium
5	Longest Palindromic Substring	Medium
6	ZigZag Conversion	Medium
8	String to Integer (atoi)	Medium
10	Regular Expression Matching	Hard
12	Integer to Roman	Medium
13	Roman to Integer	Easy
14	Longest Common Prefix	Easy
17	Letter Combinations of a Phone Number	Medium
20	Valid Parentheses	Easy
22	Generate Parentheses	Medium
28	Implement strStr()	Easy
30	Substring with Concatenation of All Words	Hard
32	Longest Valid Parentheses	Hard
38	Count and Say	Easy
43	Multiply Strings	Medium
44	Wildcard Matching	Hard
49	Group Anagrams	Medium
58	Length of Last Word	Easy
65	Valid Number	Hard
67	Add Binary	Easy
68	Text Justification	Hard
71	Simplify Path	Medium
72	Edit Distance	Hard
76	Minimum Window Substring	Hard
87	Scramble String	Hard
91	Decode Ways	Medium
93	Restore IP Addresses	Medium
97	Interleaving String	Hard
115	Distinct Subsequences	Hard