easy(173/237+x) medium(144/437+x) hard(4/x)
1.Two Sum(dict)
7.(skip)(math)
9.(skip)(string trick)
11.Container with Most Water
12.(skip)(bad problem)
13.(skip)(brute force)
14.(skip)(bad problem)
17.Letter Combination of a Phone Number
20.Valid Parentheses
21.Merge Two LL
22.Generate Parentheses
24/LL.Swap Nodes in Pairs
26.(skip)(bad problem)
27.(skip)(bad problem)
29.(skip)(bad problem)
34.Find First and last element in an array
35.Search Insert Position
38.(skip)(bad problem)
39/Sum.Combination Sum
40/Sum.Combination Sum 2
46.Permutations(backstring)
47/46.Permutations 2
48.Rotate Matrix
49.Group Anagram
50.(skip)(bad problem)
53.Maximum Subarray
54/59.Spiral Matrix
55.Jump Game
57.Insert Intervals
58.(skip)(python trick)
59.Spiral Matrix 2(brute force)
62.Unique Paths
63/62.Unique Paths 2
64.Minimum Path Sum(dp)
66.(skip)(trick)
67.(skip)(bit manipulation)
69.(skip)(math)
70.Climbing Stairs
73.Set Matrix Zeroes
75.Sort Colors
77.Combinations
78.Subsets(backtracking)
80.(skip)(bad problem)
83.Remove duplicates from sorted LL
87.(skip)(bad problem)
88.(skip)(bad problem)
89.(skip)(bad problem)
90/78.Subsets 2
94/BT.BT Inorder Traversal
96/BST.Unique BST
100/BT.Same Tree
101.Symmetric Tree(two times traversal)
102/BT.BT level order Traversal
103/BT.BT zigzag Trversal
104.Maximum Depth of Binary Tree
105/BT.Construct BT from inorder and preorder traversal
106/BT.Construct BT from inorder and postorder traversal
107.(skip)(same as BFS)
108/BST.Convert sorted Array to BST
111.Minimum Depth
112/BT.Path Sum
113/BT.Path Sum 2
114/BT.Flattern Bt to LL
118.Pascal’s Triangle
119.Pascal’s Triangle 2 (-118)
122.(skip)(bad problem)
125.(skip)(bad problem)
129/BT.Sum Root to Leaf Numbers
131/Palindrome.Palindrome partition
136.Single Number
137.(skip)(bit manipulation)
141.LL Cycle
144/BT.BT Preorder Traversal
153.Find Minimum in Rotated Sorted Array
162.(skip)(bad problem)
165.(skip)(bad problem)
166.(skip)(bad problem)
167.Two Sum 2 - sorted array
168.(skip)(brute force)
169.(skip)(easy dict)
171.(skip)(brute force)
189.Rotate Array
191.(skip)(bit manipulation)
198.House Robber(dp)
199/BT.BT right side view
202.Happy Number
203.Remove Elements in LL
205.Isomorphic Strings
206.Reverse Linked List(LL base)
213/198.House Robber2(dp)
215.Kth Largest number in an array(to do again)
216.Combination Sum 3
217.Contain Duplicates 1 (skip)(dict)
219.Contain Duplicates 2
223.Rectangle Area
226.Invert Binary Tree
230/BST.K-th Smallest element in BST
231.Power of Two(skip)(easy)
234/LL.Palindrome LL
235.Lowest Common Ancestor of a BST
237.(skip)(bad problem)
238.Product of Array Except Self
240.Search a 2D matrix 2
242.(skip)(brute force)(dict)
257/BT.Binary Tree Path
258.(skip)(bad problem)
260.Single Number 3(skip)(to be optimized)
263.(skip)(bad problem)
268.(skip)(math)(bad problem)
274.(skip)(bad problem)
275.(skip)(bad problem)
278.Find bad version(binary search)
283.Move Zeroes
287.Find the Duplicate Number
290.Word Pattern (same as 205)
292.(skip)(bad problem)
300.Longest Increasing Subsequence
303.Range Sum Query
309.Best Time to Buy and Sell with Cooldown
319.(dkip)(bad problem)
322.Coin change(backpack problem)
326.(skip)(math)
328/LL.Odd Even LL
334.Increasing Triplet Subsequent
338.Counting Bits
342.Power of Four(skip)
343.Integer Break
344.Reverse String (skip)(python trick)
345.(skip)(bad problem)
347/451.Top K Frequent Elements(similar as 451)
349.(skip)(bad problem)
357.(skip)(bad problem)
365.(skip)(bad problem)
367.(skip)(trick)(binary search)
371.(skip)(bit manipulation)
372.(skip)(bad problem)
374.(skip)(bad problem)(binary search)
375.(skip)(bad problem)
377/Sum.Combination Sum 4
378.Kth smallest element in sorted matrix(heap)
383.(skip)(easy dict)
384.(skip)(bad problem)
386.(skip)(str-int tricl
387.First Unique Character in String(dict)
388.(skip)(bad problem)
389.Fine the Difference
390.(skip)(bad problem)
392.Is Subsequence
393.(skip)(bad problem)
397.(skip)(bad problem)
398.(skip)(bad problem)
400.(skip)(math
401.(skip)
404.Sum of Left Leaves
409/Palin.Longest Palindrome(count)(brute force)
412.Fizz Buzz (skip)(brute force)
414.(skip)(bad problem)
415.(skip)（底层操作）
416/698.Partition Equal Sum Subsets
420.(skip)(bad problem)
423.(skip)(bad problem)
424.Longest Repeating Char Replacement(slide window)
427.(skip)(bad)(dfs)
429.N-ary Tree Level Order Traversal
434.(skip)(bad problem)
435.Non-overlapping Interval
441.(skip)(bad problem)(math)
442/448.Find All Duplicates in an Array(similar as 448)
443.(skip)(bad broblem)(two pointer)
447.(skip)(bad problem)
448.Find all Numbers Disappeared in an Array
451.Sort Character By frequency
452.Minimum Number of Arrows to Burst Ballons(求交集）
453.(skip)(math problem)
455.Assign Cookies(two pointers)
458.(skip)(bad problem)(math)
459.Repeated Substring Pattern(trick)
461.Hamming Distance (To do)
462.(skip)(math)
463.Island Perimeter
470.Implement Rand10 using Rand7
474.Ones and Zeros
476.(skip)(bit manipulation)
477.Total Hamming Distance(skip)(bit manipulation)(string trick)
479.(skip)(bad problem)(math)
481.(skip)(bad problem)
482.(skip)(bad problem)
483.(skip)(bad problem)(math)
485.(skip) (brute force)
491/78.Increasing Subsequence
492.(skip)(brute force)
494/Sum.Target Sum
495.(skip)(bad problem)
496.Next Greater Element 1 (skip)
498.Diagonal Traverse(skip)
500.Keyboard Row (skip)(bad)
501.Find Mode in BST
503.Next Greater Element 2(stack)
504.base 7
506.(skip)(bad problem)
507.(skip)(math)
508/BT.Most Frequent Subtree Sum
513/BT.Find Bottom Left Tree Value(Similar as 637)(BFS)
515/BT.Find Largest value in each Tree Row(similar as 637)
516/Palin.Longest Palindrome Subsequence
518.Coin Change 2
520.(skip)(brute force)
521.(skip)(bad problem)
522.(skip)(bad problem)
524.Longest Word in Dic Trough Deleting
530.Minimum absolute Difference in BST
535.(skip)(bad problem)
537.(skip)(bad problem)
539.Minimum Time Difference
540.Single Element in Sorted Array
541.(skip)(bad problem)(brute force)
543.Diameter of Binary Tree
551.(skip)(bad problem)
553.(skip)(bad problem)
554.Brick Wall(hash table)
556.Reshape the Matrix
557.Reverse words in a String 3
558.(skip)(bad problem)
559.Maximum Depth of N-ary Tree
560.Subarray Sum Equal to K
561.Array Partition 1
563.Binary Tree Tilt(bad)
565.Array Nesting
575.Distribute Candies (skip)(bad)
583.Delete Operation for Two Strings
589.N-ary Tree Preorder Traversal
590.N-ary Tree Postorder Traversal
593.(skip)(bad problem)
594.Longest harmonious Subsequence(dict)
598.(skip)(brute force)
599.Min Index Sum of Two Lists(dict)(brute force)
617.Merge Two Binary Trees
622.Design Circular Queue
623/BT.Add One Row to Tree
633.Sum of Square Numbers
636.(skip)(bad problem)
637.Average of Levels in Binary Tree
638.(skip)(bad problem)
640.(skip)(bad problem)
643.Maximum Average Subarray 1
645.(skip)(dict)
646.Maximum Length of Pair Chain
647/Palin.Palindromic Substrings(dp)
650.2 Keys Keyboard(dp)
652/BT.Find Duplicate Subtrees
654.Maximum BT
655.(skip)(bad problem)
657.Robot Return To Origin (skip)(dict)
661.(skip)(bad problem)(brute force)
662/BT,Maximum width of BT
669.Trim a Binary Search Tree
670.Maximum Swap
671.Second Minimum Node In a BT
672.(skip)(bad problem)
674.Longest Continuous Increasing Subsequence(same as continuous ones)
680/Palin.Valid Palindrome 2
682.Baseball Game (skip)(bad)
686.Repeated String Match
690.(skip)(bad)
692.Top K Frequent Words
693.(skip)(bit manipulation)
697.Degree of an Array(brute force)(bad)
698.Partition to K equals sum subsets
700.Search in a Binary Searcch Tree
701/BST.Insert into a BST
704.Binary Search
705.Design Hashset
709.To Lower Case (skip)(bad)
717.(skip)(bad problem)
718.Maximum Length of Repeated Subarray(dp)(to do again)
720.(skip)(bad problem)
724.Find Pivot Index(trick)
725/LL.Split LL in Parts
728.Self Dividing Numbers
739.Daily Temperature(stack)
740.Delete and Earn
744.(skip)(binary search)
747.(skip)(dict)(brute force)
748.(skip)(bad problem)
762.(skip)(bit manipulation)
763.Partition Labels
766.Toeplitz Matrix
771.Jewels and Stones
781.(skip)(math)
783.(skip)(same with 530)
784.Letter Case Permutation
788.(skip)(bad problem)
789.(skip)(bad problem)(math)
791.Custom Sort String
795.Number of Subarray with Bounded Maximum
796.Rotate String (trick)
804.Unique Morse Code Words (skip）(brute force)
806.Number of Lines To Write String (skip)(bad)
808.(skip)(bad problem)
809.(skip)(bad problem)
811.Subdomain Visit Count (skip) (brute force)
812.(skip)(bad problem)
814/BT.BT prunning
816.(skip)(bad problem)
817.(skip)(bad problem)
819.(skip)(bad problem)
820.Short Encoding of Words
821.Shortest Distance to a Character
822.(skip)(bad problem)
824.(skip)(brute force)
825.(skip)(bad problem)
830.Position of Large Groups(mind the margin)
831.(skip)(bad problem)
832.Flipping an Image
833.(skip)(bad problem)
836.Rectangle Overlap
840.(skip)(bad problem)
844.Backspace String(stack)
846.Hand of Straights
849.Maximum Distance to Closet Person
851.Loud and Rich(skip)(bad problem)
852.Peak Index in a Mountain Array (skip)(bad problem)
856.Score of Parentheses
858.(skip)(math)
859.Buddy String
860.Lemonade Change(brute force)
866.(skip)(bad problem)
868.Binary Gap (skip)(bin manipulation)
872.Leaf-similar Trees
874.(skip)(bad problem)
876.Middle of the Linked List
883.Projection Area of 3D shapes
884.Uncommon Words from Two Sentences
888.Fair Candy Swap
889/BT.Construct BT from pre and post traversal
890/205.Find and Replace Pattern(based on 205)
893.Groups of Special-Equivalent Strings
896.Monotonic Array
908.(skip)(bad problem)
909.(skip)(bad problem)
915.Partition Array into Disjoint Intervals
917.Reverse Only Letters