Top frequency Leetcode summary

. Binary Search

#	Title	Solution	Difficulty	Source Code	Page
4	Median of Two Sorted Arrays		Hard	FindMedianSortedArrays.java
29	Divide Two Integers		Medium	Divide.java
33	Search in Rotated Sorted Array		Medium	Search.java
34	Find First and Last Position of Element in Sorted Array		Medium	SearchRange.java
50	Pow(x, n)		Medium	myPow.java
69	Sqrt(x)		Easy	MySqrt.java
74	Search a 2D Matrix		Medium	SearchMatrix.java
162	Find Peak Element		Medium	FindPeakElement.java
209	Minimum Size Subarray Sum		Medium	MinSubArrayLen.java
230	Kth Smallest Element in a BST		Medium	KthSmallest.java
240	Search a 2D Matrix II		Medium	SearchMatrix2.java
278	First Bad Version		Easy	FirstBadVersion.java
300	Longest Increasing Subsequence		Medium	Longest.java
315	Count of Smaller Numbers After Self		Hard	CountSmaller.java
354	Russian Doll Envelopes		Hard	MaxEnvelopes.java
363	Max Sum of Rectangle No Larger Than K		Hard	MaxSumSubmatrix.java
493	Reverse Pairs		Hard	ReversePairs.java
528	Random Pick with Weight		Medium	PickIndex.java
981	Time Based Key-Value Store		Medium	TimeMap.java
1235	Maximum Profit in Job Scheduling		Hard	JobScheduling.java
1283	Find the Smallest Divisor Given a Threshold		Medium	SmallestDivisor.java

. Sorting

#	Title	Solution	Difficulty	Source Code	Page
56	Merge Intervals		Medium	MergeIntervals.java
75	Sort Colors		Medium	SortColors.java
148	Sort List		Medium	SortList.java
179	Largest Number		Medium	LargestNumber.java
253	Meeting Rooms II		Medium	MinMeetingRooms.java
324	Wiggle Sort II		Medium	WiggleSort.java
767	Reorganize String		Medium	Reorganizestring.java
973	K Closest Points to Origin		Medium	KClosest.java
1152	Analyze User Website Visit Pattern		Medium	MostVisitedPattern.java
1229	Meeting Scheduler		Medium	MinAvailableDuration.java
1244	Design A Leaderboard		Medium	Leaderboard.java
1353	Maximum Number of Events That Can Be Attended		Medium	MaxEvents.java
1383	Maximum Performance of a Team		Hard	Sorting
1481	Least Number of Unique Integers after K Removals		Medium	FindLeastNumOfUniqueInts.java

. Recursion

#	Title	Solution	Difficulty	Source Code	Page
395	Longest Substring with At Least K Repeating Characters		Medium	LongestSubstring.java
726	Number of Atoms		Hard	Recursion
761	Special Binary String		Hard	Recursion

. LinkedList

#	Title	Solution	Difficulty	Source Code	Page
2	Add Two Numbers		Medium	AddTwoNumbers.java
19	Remove Nth Node From End of List		Medium	RemoveNthFromEnd.java
21	Merge Two Sorted Lists		Easy	MergeTwoLists.java
23	Merge k Sorted Lists		Hard	MergeKLists.java
25	Reverse Nodes in k-Group		Hard	ReverseKGroup.java
86	Partition List		Medium	Partition.java
92	Reverse Linked List II		Medium	ReverseBetween.java
138	Copy List with Random Pointer		Medium	CopyRandomList.java
141	Linked List Cycle		Easy	HasCycle.java
142	Linked List Cycle II		Medium	GetIntersect.java
143	Reorder List		Medium	ReorderList.java
160	Intersection of Two Linked Lists		Easy	GetIntersectionNode.java
203	Remove Linked List Elements		Easy	RemoveElements.java
206	Reverse Linked List		Easy	ReverseList.java
234	Palindrome Linked List		Easy	IsPalindromeList.java
237	Delete Node in a Linked List		Easy	DeleteNode.java
328	Odd Even Linked List		Medium	OddEvenList.java
426	Convert Binary Search Tree to Sorted Doubly Linked List		Medium	TreeToDoublyList.java
445	Add Two Numbers II		Medium	AddTwoNumbersII.java

. Stack and queue

#	Title	Solution	Difficulty	Source Code	Page
20	Valid Parentheses		Easy	IsValidParentheses.java
71	Simplify Path		Medium	SimplifyPath.java
84	Largest Rectangle in Histogram		Hard	LargestRectangleArea.java
85	Maximal Rectangle		Hard	MaximalRectangle.java
150	Evaluate Reverse Polish Notation		Medium	EvalRPN.java
155	Min Stack		Easy	MinStack.java
173	Binary Search Tree Iterator		Medium	BSTIterator.java
218	the-skyline-problem		Medium	GetSkyline.java
224	Basic Calculator		Hard	Calculate1.java
227	Basic Calculator II		Medium	Calculate2.java
341	Flatten Nested List Iterator		Medium	NestedIterator.java
346	Moving Average from Data Stream		Easy	MovingAverage.java
394	Decode String		Medium	DecodeString.java
503	Next Greater Element II		Medium	NextGreaterElements.java
636	Exclusive Time of Functions		Medium	ExclusiveTime.java
735	Asteroid Collision		Medium	AsteroidCollision.java
739	Daily Temperatures		Medium	DailyTemperatures.java
770	Basic Calculator IV		Hard	Stack
856	Score of Parentheses		Medium	ScoreOfParentheses.java
901	Online Stock Span		Medium	StockSpanner.java
1130	Minimum Cost Tree From Leaf Values		Medium	MctFromLeafValues.java
1209	Remove All Adjacent Duplicates in String II		Medium	RemoveDuplicatesII.java
1249	Minimum Remove to Make Valid Parentheses		Medium	MinRemoveToMakeValid.java

. Tree

#	Title	Solution	Difficulty	Source Code	Page
102	Binary Tree Level Order Traversal		Medium	Binary Tree Level Order Traversal	-----------
104	Maximum Depth of Binary Tree		Easy	MaxDepth.java	-----------
94	Binary Tree Inorder Traversal		Medium	InorderTraversal.java
98	Validate Binary Search Tree		Medium	IsValidBST.java
101	Symmetric Tree		Easy	IsSymmetric.java
102	Binary Tree Level Order Traversal		Medium	LevelOrder.java
103	Binary Tree Zigzag Level Order Traversal		Medium	ZigzagLevelOrder.java
104	Maximum Depth of Binary Tree		Easy	MaxDepth.java
105	Construct Binary Tree from Preorder and Inorder Traversal		Medium	BuildTree.java
108	Convert Sorted Array to Binary Search Tree		Easy	SortedArrayToBST.java
116	Populating Next Right Pointers in Each Node		Medium	Connect.java
199	Binary Tree Right Side View		Medium	RightSideView.java
226	Invert Binary Tree		Easy	InvertTree.java
236	Lowest Common Ancestor of a Binary Tree		Medium	LowestCommonAncestor1.java
285	Inorder Successor in BST		Medium	InorderSuccessor.java
366	Find Leaves of Binary Tree		Medium	FindLeaves.java
297	Serialize and Deserialize Binary Tree		Hard	Codec.java
543	Diameter of Binary Tree		Easy	DiameterOfBinaryTree.java
545	Boundary of Binary Tree		Medium	BoundaryOfBinaryTree.java
572	Subtree of Another Tree		Easy	IsSubtree.java
863	All Nodes Distance K in Binary Tree		Medium	DistanceK.java
987	Vertical Order Traversal of a Binary Tree		Hard	VerticalTraversal.java

. HashMap, Array, String

#	Title	Solution	Difficulty	Source Code	Page
1	Two Sum		Easy	Two Sum
3	Longest Substring Without Repeating Characters		Medium	LengthOfLongestSubstring.java
6	ZigZag Conversion		Medium	ZigZagConvert.java
8	String to Integer (atoi)		Medium	MyAtoi.java
11	Container With Most Water		Medium	MaxArea.java
12	Integer to Roman		Medium	IntToRoman.java
13	Roman to Integer		Easy	RomanToInt.java
14	Longest Common Prefix		Easy	LongestCommonPrefix.java
15	3Sum		Medium	ThreeSum.java
16	3Sum Closest		Medium	ThreeSumClosest.java
26	Remove Duplicates from Sorted Array		Easy	RemoveDuplicates.java
28	Implement strStr()		Easy	StrStr.java
31	Next Permutation	String Operation / Math	Medium	NextPermutation.java	-----------
36	Valid Sudoku		Medium	IsValidSudoku.java
37	Sudoku Solver		Hard	SolveSudoku.java
38	Count and Say		Medium	CountAndSay.java
39	Combination Sum		Medium	CombinationSum.java
41	First Missing Positive		Hard	FirstMissingPositive.java
43	Multiply Strings		Medium	Multiply.java
48	Rotate Image		Medium	Rotate.java
49	Group Anagrams		Medium	GroupAnagrams.java
54	Spiral Matrix		Medium	SpiralOrder.java
65	Valid Number		Hard	IsNumber.java
66	Plus One		Easy	PlusOne.java
67	Add Binary		Easy	AddBinary.java
68	Text Justification		Hard	FullJustify.java
73	Set Matrix Zeroes		Medium	SetZeroes.java
76	Minimum Window Substring		Hard	MinWindow.java	!!!Lai
88	Merge Sorted Array		Easy	Merge.java
118	Pascal's Triangle		Easy	Generate.java
122	Best Time to Buy and Sell Stock II		Easy	MaxProfit2.java
125	Valid Palindrome		Easy	IsPalindrome.java
136	Single Number		Easy	SingleNumber.java
149	Max Points on a Line		Hard	MaxPoints.java
151	Reverse Words in a String		Medium	ReverseWords.java
152	Maximum Product Subarray		Medium	MaxProduct.java
158	Read N Characters Given Read4 II - Call multiple times		Hard	String
163	Missing Ranges		Easy	FindMissingRanges.java
166	Fraction to Recurring Decimal		Medium	FractionToDecimal.java
169	Majority Element		Easy	MajorityElement.java
189	Rotate Array		Medium	Rotate0.java
202	Happy Number		Easy	IsHappy.java
204	Count Primes		Easy	CountPrimes.java
217	Contains Duplicate		Easy	ContainsDuplicate.java
238	Product of Array Except Self		Medium	ProductExceptSelf.java
242	Valid Anagram		Easy	IsAnagram.java
243	Shortest Word Distance		Easy	ShortestWordDistance.java
244	Shortest Word Distance II		Medium	WordDistance.java
244	Shortest Word Distance II		Medium	WordDistance.java
268	Missing Number		Easy	MissingNumber.java
273	Integer to English Words		Hard	NumberToWords.java
277	Find the Celebrity		Medium	FindCelebrity.java
283	Move Zeroes		Easy	MoveZeroes.java
287	Find the Duplicate Number		Medium	FindDuplicate287.java
289	Game of Life		Medium	GameOfLife.java
340	Longest Substring with At Most K Distinct Characters		Medium	LengthOfLongestSubstringKDistinct.java
344	Reverse String		Easy	ReverseString.java	-----------
347	Top K Frequent Elements		Medium	topKFrequent.java
350	Intersection of Two Arrays II		Easy	Intersect.java
356	Line Reflection		Medium	IsReflected.java
380	Insert Delete GetRandom O(1)		Medium	RandomizedSet.java
381	Insert Delete GetRandom O(1) - Duplicates allowed		Hard	RandomizedCollection.java
387	First Unique Character in a String		Easy	FirstUniqChar.java
415	Add Strings		Easy	AddStrings.java
438	Find All Anagrams in a String	Sliding window	Medium	Find All Anagrams in a String
442	Find All Duplicates in an Array		Medium	FindDuplicates.java
443	String Compression		Medium	Compress443.java
454	4Sum II		Medium	FourSumCount.java
509	Fibonacci Number		Easy	Fib.java
523	Continuous Subarray Sum		Medium	CheckSubarraySum.java	HashMap
532	K-diff Pairs in an Array		Medium	FindPairs.java
535	Encode and Decode TinyURL		Medium	Codec.java
539	Minimum Time Difference		Medium	FindMinDifference.java
560	Subarray Sum Equals K		Medium	SubarraySum.java
564	Find the Closest Palindrome		Hard	String
581	Shortest Unsorted Continuous Subarray		Medium	FindUnsortedSubarray.java
609	Find Duplicate File in System		Medium	FindDuplicate.java
621	Task Scheduler		Medium	LeastInterval.java	pages
647	Palindromic Substrings		Medium	CountSubstrings.java
665	Non-decreasing Array		Medium	CheckPossibility.java
670	Maximum Swap		Medium	MaximumSwap.java
680	Valid Palindrome II		Easy	ValidPalindrome2.java
692	Top K Frequent Words		Medium	TopKFrequent.java
723	Candy Crush		Medium	CandyCrush.java
724	Find Pivot Index		Easy	PivotIndex.java
729	My Calendar I		Medium	MyCalendar1.java
811	Subdomain Visit Count		Easy	SubdomainVisits.java
937	Reorder Data in Log Files		Easy	ReorderLogFiles.java
953	Verifying an Alien Dictionary		Easy	IsAlienSorted.java
974	Subarray Sums Divisible by K		Medium	SubarraysDivByK.java
1010	Pairs of Songs With Total Durations Divisible by 60		Medium	NumPairsDivisibleBy60.java
1048	Longest String Chain		Medium	longestStrChain.java
1146	Snapshot Array		Medium	SnapshotArray.java
1163	Last Substring in Lexicographical Order		Hard	String
1328	Break a Palindrome		Medium	BreakPalindrome.java
1423	Maximum Points You Can Obtain from Cards		Medium	MaxScore.java
1428	Leftmost Column with at Least a One		Medium	LeftMostColumnWithOne.java
1465	Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts		Medium	MaxArea1456.java
1480	Running Sum of 1d Array		Easy	RunningSum.java
1531	String Compression II		Hard	String
1570	Dot Product of Two Sparse Vectors		Medium	SparseVector.java

. BFS

#	Title	Solution	Difficulty	Source Code	Page
45	Jump Game II		Medium	Jump2.java
126	Word Ladder II		Hard	BFS
127	Word Ladder		Hard	Word Ladder
133	Clone Graph		Medium	CloneGraph.java
200	Number of Islands		Medium	Number of Islands
207	Course Schedule		Medium	Course Schedule
210	Course Schedule II		Medium	Course Schedule II
286	Walls and Gates		Medium	WallsAndGates.java
301	Remove Invalid Parentheses		Hard	RemoveInvalidParentheses.java
323	Number of Connected Components in an Undirected Graph		Medium	CountComponents.java
339	Nested List Weight Sum		Medium	DepthSum.java
378	Kth Smallest Element in a Sorted Matrix		Medium	KthSmallest.java
417	Pacific Atlantic Water Flow		Medium	PacificAtlantic.java
752	Open the Lock		Medium	OpenLock.java
909	Snakes and Ladders		Medium	BFS
994	Rotting Oranges		Medium	OrangesRotting.java
1197	Minimum Knight Moves		Medium	MinKnightMoves.java
1233	Remove Sub-Folders from the Filesystem		Medium	RemoveSubfolders.java
1242	Web Crawler Multithreaded		Medium	Crawl.java
1293	Shortest Path in a Grid with Obstacles Elimination		Hard	ShortestPath.java

. DFS

#	Title	Solution	Difficulty	Source Code	Page
17	Letter Combinations of a Phone Number		Medium	LetterCombinations.java
22	Generate Parentheses		Medium	GenerateParenthesis.java
78	Subsets		Medium	Subsets0.java
79	Word Search		Medium	WordSearch.java
99	Recover Binary Search Tree		Hard	DFS
124	Binary Tree Maximum Path Sum		Hard	DFS
130	Surrounded Regions		Medium	Solve.java
211	Design Add and Search Words Data Structure		Medium	WordDictionary.java
329	Longest Increasing Path in a Matrix		Hard	LongestIncreasingPath.java
332	Reconstruct Itinerary		Medium	FindItinerary.java
364	Nested List Weight Sum II		Medium	DepthSumInverse.java
472	Concatenated Words		Hard	DFS
489	Robot Room Cleaner		Hard	DFS
526	Beautiful Arrangement		Medium	CountArrangement.java
529	Minesweeper		Medium	UpdateBoard.java
547	Number of Provinces		Medium	FindCircleNum.java
695	Max Area of Island		Medium	MaxAreaOfIsland.java
698	Partition to K Equal Sum Subsets		Medium	CanPartitionKSubsets.java
721	Accounts Merge		Medium	AccountsMerge.java
797	All Paths From Source to Target		Medium	AllPathsSourceTarget.java
1192	Critical Connections in a Network		Hard	CriticalConnections.java

. DP

#	Title	Solution	Difficulty	Source Code	Page
96	Unique Binary Search Trees		Medium	NumTrees.java	-----------
5	Longest Palindromic Substring		Medium	LongestPalindrome.java
10	Regular Expression Matching		Hard	DP
32	Longest Valid Parentheses		Hard	DP
42	Trapping Rain Water		Hard	Trap.java
44	Wildcard Matching		Hard	IsMatch.java
53	Maximum Subarray		Easy	MaxSubArray.java
55	Jump Game		Medium	CanJump.java
62	Unique Paths		Medium	UniquePaths.java
64	Minimum Path Sum		Medium	MinPathSum.java
70	Climbing Stairs		Easy	ClimbStairs.java
72	Edit Distance		Hard	MinDistance.java
91	Decode Ways		Medium	NumDecodings.java
115	Distinct Subsequences		Hard	NumDistinct.java
121	Best Time to Buy and Sell Stock		Easy	MaxProfit.java
123	Best Time to Buy and Sell Stock III		Hard	MaxProfit3.java
128	Longest Consecutive Sequence		Hard	LongestConsecutive.java
131	Palindrome Partitioning		Medium	Partition.java
134	Gas Station		Medium	CanCompleteCircuit.java
139	Word Break		Medium	WordBreak.java
140	Word Break II		Hard	WordBreak2.java
188	Best Time to Buy and Sell Stock IV		Hard	MaxProfit4.java
198	House Robber		Medium	Rob.java
221	Maximal Square		Medium	Largest.java	DP
256	Paint House		Medium	MinCost.java
265	Paint House II		Hard	MinCostII.java
279	Perfect Squares		Medium	NumSquares.java
309	Best Time to Buy and Sell Stock with Cooldown		Medium	MaxProfit5.java
312	Burst Balloons		Hard	MaxCoins.java
322	Coin Change		Medium	CoinChange.java
334	Increasing Triplet Subsequence		Hard	IncreasingTriplet.java
338	Counting Bits		Medium	CountBits.java
403	Frog Jump		Hard	canCross.java
322	Coin Change		Medium	CoinChange.java
416	Partition Equal Subset Sum		Medium	CanPartition.java
494	Target Sum		FindTargetSumWays.java	DP
518	Coin Change 2		Medium	CoinChange.java
718	Maximum Length of Repeated Subarray		Medium	FindLength.java
741	Cherry Pickup		Hard	DP
871	Minimum Number of Refueling Stops		Hard	DP
920	Number of Music Playlists		Hard	DP
1220	Count Vowels Permutation		Hard	DP
1326	Minimum Number of Taps to Open to Water a Garden		Hard	DP
1335	Minimum Difficulty of a Job Schedule		Hard	DP
1345	Jump Game IV		Hard	MinJumps4.java
1359	Count All Valid Pickup and Delivery Options		Hard	DP

. Design

#	Title	Solution	Difficulty	Source Code	Page
146	LRU Cache		Medium	LRUCache.java]
208	Implement Trie (Prefix Tree)		Medium	Trie.java
251	Flatten 2D Vector		Medium	Vector2D.java
295	Find Median from Data Stream		Hard	MedianFinder.java
348	Design Tic-Tac-Toe		Medium	TicTacToe.java
355	Design Twitter		Medium	Twitter.java
359	Logger Rate Limiter		Easy	Logger.java
362	Design Hit Counter		Medium	HitCounter.java
384	Shuffle an Array		Medium	Shuffle.java
460	LFU Cache		Hard	LFUCache.java
588	Design In-Memory File System		Hard	FileSystem.java
631	Design Excel Sum Formula		Hard	Excel.java
642	Design Search Autocomplete System		Hard	AutocompleteSystem.java	pages
716	Max Stack		Easy	MaxStack.java
1348	Tweet Counts Per Frequency		Medium	TweetCounts.java
1396	Design Underground System		Medium	UndergroundSystem.java
1472	Design Browser History		Medium	BrowserHistory.java

. Trie

#	Title	Solution	Difficulty	Source Code	Page
692	Top K Frequent Words		Medium	Trie	692
212	Word Search II		Hard	FindWords2.java
211	Design Add and Search Words Data Structure		Medium	WordDictionary.java
642	Design Search Autocomplete System		Hard	Trie
472	Concatenated Words		Hard	Trie
208	Implement Trie (Prefix Tree)		Medium	Trie.java
336	Palindrome Pairs		Hard	Trie
421	Maximum XOR of Two Numbers in an Array		Medium	findMaximumXOR.java
676	Implement Magic Dictionary		Medium	MagicDictionary.java
425	Word Squares		Hard	Trie