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#	Title	Difficulty	Frequency
1	Two Sum	Easy	0.69
4	Median of Two Sorted Arrays	Hard	2.32
7	Reverse Integer	Medium	0.83
9	Palindrome Number	Easy	1.06
13	Roman to Integer	Easy	6.01
14	Longest Common Prefix	Easy	0.66
15	3Sum	Medium	1.30
21	Merge Two Sorted Lists	Easy	2.51
31	Next Permutation	Medium	3.53
34	Find First and Last Position of Element in Sorted Array	Medium	2.44
49	Group Anagrams	Medium	1.88
50	Pow(x, n)	Medium	2.25
54	Spiral Matrix	Medium	1.61
56	Merge Intervals	Medium	7.07
65	Valid Number	Hard	14.21
71	Simplify Path	Medium	3.85
76	Minimum Window Substring	Hard	2.02
78	Subsets	Medium	1.48
88	Merge Sorted Array	Easy	1.12
121	Best Time to Buy and Sell Stock	Easy	0.81
125	Valid Palindrome	Easy	1.34
128	Longest Consecutive Sequence	Medium	0.87
129	Sum Root to Leaf Numbers	Medium	5.41
138	Copy List with Random Pointer	Medium	15.25
146	LRU Cache	Medium	4.65
162	Find Peak Element	Medium	3.61
199	Binary Tree Right Side View	Medium	3.46
215	Kth Largest Element in an Array	Medium	20.94
217	Contains Duplicate	Easy	0.47
219	Contains Duplicate II	Easy	2.30
227	Basic Calculator II	Medium	72.86
234	Palindrome Linked List	Easy	1.54
236	Lowest Common Ancestor of a Binary Tree	Medium	16.82
240	Search a 2D Matrix II	Medium	3.62
249	Group Shifted Strings	Medium	27.76
283	Move Zeroes	Easy	1.84
301	Remove Invalid Parentheses	Hard	14.73
314	Binary Tree Vertical Order Traversal	Medium	116.31
383	Ransom Note	Easy	1.73
408	Valid Word Abbreviation	Easy	43.96
435	Non-overlapping Intervals	Medium	3.77
490	The Maze	Medium	20.80
494	Target Sum	Medium	3.46
543	Diameter of Binary Tree	Easy	8.48
560	Subarray Sum Equals K	Medium	1.77
680	Valid Palindrome II	Easy	54.94
721	Accounts Merge	Medium	16.34
766	Toeplitz Matrix	Easy	14.11
528	Random Pick with Weight	Medium	27.28
973	K Closest Points to Origin	Medium	3.42
987	Vertical Order Traversal of a Binary Tree	Hard	10.47
1091	Shortest Path in Binary Matrix	Medium	6.20
1249	Minimum Remove to Make Valid Parentheses	Medium	37.65
1492	The kth Factor of n	Medium	6.29
1570	Dot Product of Two Sparse Vectors	Medium	51.99
1650	Lowest Common Ancestor of a Binary Tree III	Medium	21.95
1762	Buildings With an Ocean View	Medium	159.77