LeetCode

Below is a summary of my solutions to the problems on LeetCode. The main idea of each problem can usually be found at the beginning of the corresponding source file. I will keep updating the list and feel free to share any of your thoughts!

#	Title	Solutions
	Maximum Performance of a Team	[ Sorting + Heap ]
	Balance a Binary Search Tree	[ In-order Traversal + Divide-and-Conquer ]
	Design a Stack With Increment Operation	[ Lazy Increment ]
	Lucky Numbers in a Matrix	[ Solution ]
	Minimum Cost to Make at Least One Valid Path in a Grid	[ SSSP ]
	Linked List in Binary Tree	[ DFS ]
	Rank Teams by Votes	[ Radix Sort ]
	How Many Numbers Are Smaller Than the Current Number	[ Counting Sort ]
	Largest Multiple of Three	[ Math ]
	Closest Divisors	[ Enumeration ]
	Validate Binary Tree Nodes	[ DFS ]
	Number of Days Between Two Dates	[ Datetime ]
	Construct Target Array With Multiple Sums	[ Backtracking ]
	Maximum Number of Events That Can Be Attended	[ Greedy + Heap/BST ]
	Product of the Last K Numbers	[ Compact Array ]
	Count Negative Numbers in a Sorted Matrix	[ Young Tableau ]
	Path with Maximum Gold	[ Backtracking ]
	Count Vowels Permutation	[ Counting ]
	Longest Arithmetic Subsequence of Given Difference	[ DP ]
	Play with Chips	[ Math ]
	Minimum Moves to Reach Target with Rotations	[ BFS ]
	Remove All Adjacent Duplicates in String II	[ Stack ]
	Get Equal Substrings Within Budget	[ Sliding Window ]
	Unique Number of Occurrences	[ Solution ]
	Smallest String With Swaps	[ Union-Find Set + Sorting ]
	Ugly Number III	[ Bisection + Inclusion-Exclusion ]
	Minimum Absolute Difference	[ Solution ]
	Sort Items by Groups Respecting Dependencies	[ Topological Sort ]
	Critical Connections in a Network	[ Find All Bridges via DFS ]
	K-Concatenation Maximum Sum	[ DP + Prefix Sum ]
	Reverse Substrings Between Each Pair of Parentheses	[ Stack ]
	Maximum Number of Balloons	[ Solution ]
	Make Array Strictly Increasing	[ DP ]
	Maximum Subarray Sum with One Deletion	[ DP ]
	Day of the Week	[ Solution ]
	Distance Between Bus Stops	[ Solution ]
	Prime Arrangements	[ Math ]
	Diet Plan Performance	[ Sliding Window ]
	Can Make Palindrome from Substring	[ Greedy ]
	Number of Valid Words for Each Puzzle	[ Bit Manipulation ]
	Invalid Transactions	[ Brute-force ]
	Compare Strings by Frequency of the Smallest Character	[ Binary Search ]
	Remove Zero Sum Consecutive Nodes from Linked List	[ Prefix Sum ]
	Dinner Plate Stacks	[ Stack + TreeSet ]
	Find Words That Can Be Formed by Characters	[ Solution ]
	Maximum Level Sum of a Binary Tree	[ DFS ]
	As Far from Land as Possible	[ BFS ]
	Last Substring in Lexicographical Order	[ Suffix Array ]
	Online Majority Element In Subarray	[ Randomization + Bisect ]
	Swap For Longest Repeated Character Substring	[ Greedy ]
	Number of Dice Rolls With Target Sum	[ Counting ]
	Day of the Year	[ Math ]
	Longest Chunked Palindrome Decomposition	[ DP ]
	Snapshot Array	[ Binary Search ]
	Binary Tree Coloring Game	[ Solution ]
	Decrease Elements To Make Array Zigzag	[ Greedy ]
	Stone Game II	[ Game Theory + DP ]
	Largest 1-Bordered Square	[ Counting ]
	Alphabet Board Path	[ Solution ]
	N-th Tribonacci Number	[ Math ]
	Minimum Cost Tree From Leaf Values	[ DP ]
	Shortest Path with Alternating Colors	[ SSSP ]
	Number of Equivalent Domino Pairs	[ Counting ]
	Maximum of Absolute Value Expression	[ Math ]
	Smallest Sufficient Team	[ DP ]
	Longest Well-Performing Interval	[ BIT ]
	Lowest Common Ancestor of Deepest Leaves	[ Tree-DP ]
	Relative Sort Array	[ Sorting ]
	Parsing A Boolean Expression	[ DFS ]
	Filling Bookcase Shelves	[ DP ]
	Path In Zigzag Labelled Binary Tree	[ Math ]
	Distribute Candies to People	[ Solution ]
	Brace Expansion II	[ Stack ]
	Find in Mountain Array	[ Binary Search ]
	Car Pooling	[ Sweep-line Algorithm ]
	Statistics from a Large Sample	[ Solution ]
	Shortest Common Supersequence	[ DP + Backtracking ]
	Shortest Path in Binary Matrix	[ BFS ]
	Largest Values From Labels	[ Greedy ]
	Duplicate Zeros	[ In-place Solution ]
	Smallest Subsequence of Distinct Characters	[ Greedy + Stack ]
	Letter Tile Possibilities	[ Solution ]
	Occurrences After Bigram	[ Solution ]
1074	Number of Submatrices That Sum to Target	[ Solution ]
1073	Adding Two Negabinary Numbers	[ Solution ]
1072	Flip Columns For Maximum Number of Equal Rows	[ Bitmask ]
1071	Greatest Common Divisor of Strings	[ Solution ]
1066	Campus Bikes II	[ Optimal Bipartite Graph Matching ]
1065	Index Pairs of a String	[ Trie ]
1064	Fixed Point	[ Solution ]
1054	Distant Barcodes	[ Distant Barcodes ]
1053	Previous Permutation With One Swap	[ Math ]
1052	Grumpy Bookstore Owner	[ Sliding Window ]
1051	Height Checker	[ Sorting ]
1049	Last Stone Weight II	[ DP ]
1048	Longest String Chain	[ DP ]
1047	Remove All Adjacent Duplicates In String	[ Brute-force ]
1046	Last Stone Weight	[ Heap ]
1044	Longest Duplicate Substring	[ Bisection + Sliding Window + Rolling Hash ]
1043	Partition Array for Maximum Sum	[ DP ]
1042	Flower Planting With No Adjacent	[ Pigeonhole Principle ]
1041	Robot Bounded In Circle	[ Solution ]
1040	Moving Stones Until Consecutive II	[ Math ]
1039	Minimum Score Triangulation of Polygon	[ DP ]
1038	Binary Search Tree to Greater Sum Tree	[ In-order Traversal ]
1037	Valid Boomerang	[ Cross Produce ]
1036	Escape a Large Maze	[ DFS ]
1035	Uncrossed Lines	[ DP ]
1034	Coloring a Border	[ DFS ]
1033	Moving Stones Until Consecutive	[ Math ]
1032	Stream of Characters	[ Trie ]
1031	Maximum Sum of Two Non-Overlapping Subarrays	[ Brute-force ]
1030	Matrix Cells in Distance Order	[ BFS ]
1029	Two City Scheduling	[ DP ]
1028	Recover a Tree From Preorder Traversal	[ Stack ]
1027	Longest Arithmetic Sequence	[ DP ]
1026	Maximum Difference Between Node and Ancestor	[ DFS ]
1025	Divisor Game	[ Game Theory ]
1024	Video Stitching	[ DP ]
1023	Camelcase Matching	[ Brute-force ]
1022	Sum of Root To Leaf Binary Numbers	[ DFS ]
1021	Best Sightseeing Pair	[ Greedy ]
1020	Number of Enclaves	[ DFS ]
1019	Next Greater Node In Linked List	[ Greedy + TreeMap ]
1018	Binary Prefix Divisible By 5	[ Math ]
1017	Convert to Base -2	[ Math ]
1016	Binary String With Substrings Representing 1 To N	[ Brute-force ]
1015	Smallest Integer Divisible by K	[ Math ]
1014	Capacity To Ship Packages Within D Days	[ Bisect ]
1013	Partition Array Into Three Parts With Equal Sum	[ Brute-force ]
1012	Numbers With Repeated Digits	[ Backtracking | Digit+Mask DP]
1010	Pairs of Songs With Total Durations Divisible by 60	[ Counting ]
1009	Complement of Base 10 Integer	[ Bit Manipulation ]
1008	Construct Binary Search Tree from Preorder Traversal	[ DFS ]
1007	Minimum Domino Rotations For Equal Row	[ Brute-force ]
1006	Clumsy Factorial	[ Stack ]
1005	Maximize Sum of Array After K Negations	[ Greedy ]
1004	Max Consecutive Ones III	[ Sliding Window ]
1003	Check If Word Is Valid After Substitutions	[ Greedy | Java Solution ]
1002	Find Common Characters	[ Counter | Java Solution ]
1001	Grid Illumination	[ 8-queen ]
1000	Minimum Cost to Merge Stones	[ DP ]
999	Available Captures for Rook	[ Solution ]
998	Maximum Binary Tree II	[ DFS ]
997	Find the Town Judge	[ Universal Sink ]
996	Number Squareful Arrays	[ Hamiltonian Path ]
995	Minimum Number of K Consecutive Bit Flips	[ Greedy ]
994	Rotting Oranges	[ BFS ]
993	Cousins in Binary Tree	[ DFS ]
992	Subarrays with K Different Integers	[ Two Sliding-windows ]
991	Broken Calculator	[ Math ]
990	Satisfiability of equality equations	[ Union-Find Set ]
989	Add to Array-Form of Integer	[ Arithmetic Addition ]
988	Smallest String Starting from Leaf	[ Solution ]
987	Vertical Order Traversal of a Binary Tree	[ DFS + Stream ]
986	Interval List Intersections	[ Linear-time Solution ]
985	Sum of Even Numbers After Queries	[ Solution ]
984	String without AAA or BBB	[ Greedy ]
983	Minimum Cost for Tickets	[ DP ]
982	Triples with Bitwise AND Equal to Zero	[ DP + Lazy Evaluation ]
981	Time Based Key-Value Store	[ HashMap + TreeMap ]
980	Unique Paths III	[ DP + Bit-compression ]
979	Distribute Coins in Binary Tree	[ Bottom-up Solution | Top-down Solution ]
978	Longest Turbulent Subarray	[ Solution ]
977	Squares of a Sorted Array	[ 1-Liner | O(n)-time Solution ]
976	Largest Perimeter Triangle	[ Greedy ]
975	Odd Even Jump	[ DP ]
974	Subarray Sums Divisible by K	[ Prefix-sum ]
973	K Closest Points to Origin	[ 1-Liner ]
968	Binary Tree Cameras	[ Tree-DP | Greedy ]
967	Numbers with Same Consecutive Differences	[ Backtracking ]
966	Vowel Spellchecker	[ Mapper ]
965	Univalued Binary Tree	[ DFS ]
964	Least Operators to Express Number	[ Math ]
963	Minimum Area Rectangle II	[ Geometry ]
962	Maximum Width Ramp	[ Sweepline + BIT | Divide-and-Conquer | Just Sort ]
961	N-Repeated-Element in Size 2N Array	[ Partition ]
960	Delete Columns to Make Sorted III	[ DP ]
959	Regions Cut By Slashes	[ Union-find-set | Anti-aliasing ]
958	Check the Completeness of a Binary Tree	[ BFS ]
957	Prison Cells After N Days	[ Math ]
956	Tallest Billboard	[ DP ]
955	Delete Columns to Make Sorted II	[ Solution with Strong Prunings | Short Solution ]
954	Array of Doubled Pairs	[ Greedy ]
953	Verifying an Alien Dictionary	[ Solution ]
952	Largest Component Size by Common Factor	[ Math + Union-find Set ]
951	Flip Equivalent Binary Trees	[ DFS ]
950	Reveal Cards in Increasing Order	[ Simulation ]
949	Largest Time for Given Digits	[ Brute-force ]
948	Bag of Tokens	[ Greedy ]
947	Most Stones Removed with Same Row or Column	[ Union-Find Set ]
946	Validate Stack Sequences	[ Stack ]
945	Minimum Increment to Make Array Unique	[ Counting ]
944	Delete Columns to Make Sorted	[ Solution ]
943	Find the Shortest Superstring	[ DP ]
942	DI String Match	[ Construction ]
941	Valid Mountain Array	[ Two-pointer ]
940	Distinct Subsequences II	[ DP ]
939	Minimum Area Rectangle	[ Solution ]
938	Range Sum of BST	[ DFS ]
937	Reorder Log Files	[ Sorting ]
936	Stamping the Sequence	[ Thinking Reversely ]
935	Knight Dialer	[ DP ]
934	Shortest Bridge	[ DFS + BFS ]
933	Number of Recent Calls	[ Monotone Queue ]
924	Minimize Malware Spread	[ DFS ]
923	3Sum with Multiplicity	[ Counting | Two-pointer ]
922	Sort Array by Parity II	[ Solution]
921	Minimum Add to Make Parentheses Valid	[ Solution]
920	Number of Music Playlists	[ DP]
919	Complete Binary Tree Inserter	[ Solution]
918	Maximum Sum Circular Subarray	[ Divide-and-Conquer | Sliding-Window + TreeMap | Sliding-Window + Monotonic-Queue ]
917	Reverse Only Letters	[ Two-Pointer ]
916	Word Subsets	[ Counting ]
915	Partition Array into Disjoint Intervals	[ Solution ]
914	X of a Kind in a Deck of Cards	[ Math ]
913	Cat and Mouse	[ Game Theory ]
911	Online Election	[ Binary Search ]
910	Smallest Range II	[ Math ]
909	Snakes and Ladders	[ BFS ]
908	Smallest Range I	[ Greedy ]
907	Sum of Subarray Minimums	[ Divide-and-Conquer | Stack ]
906	Super Palindromes	[ Solution ]
905	Sort Array By Parity	[ 1-Liner ]
904	Fruit Into Baskets	[ Sliding-window ]
903	Valid Permutations for DI Sequence	[ DP ]
902	Numbers At Most N Given Digit Set	[ Math ]
901	Online Stock Span	[ Monotone-Stack ]
900	RLE Iterator	[ Solution ]
899	Orderly Queue	[ Math ]
898	Bitwise ORs of Subarrays	[ Divide-and-Conquer | Another Solution ]
897	Increasing Order Search Tree	[ In-order Traversal ]
896	Monotonic Array	[ 1-Liner ]
891	Sum of Subsequences Widths	[ Math ]
890	Find and Replace Pattern	[ Greedy ]
889	Construct Binary Tree from Preorder and Postorder Traversal	[ DP | Easy Solution ]
888	Fair Candy Swap	[ Solution ]
887	Super Egg Drop	[ DP with Binary Search Optimization ]
886	Possible Bipartition	[ DFS ]
885	Spiral Matrix III	[ Solution ]
884	Uncommon Words from Two Sentences	[ Solution ]
883	Projection Area of 3D Shapes	[ Solution ]
882	Reachable Nodes in Subdivided Graph	[ Shortest Path + Greedy ]
881	Boats to Save People	[ Greedy ]
880	Decoded String at Index	[ DP ]
879	Profitable Schemes	[ DP ]
878	Nth Magical Number	[ Binary Search ]
877	Stone Game	[ DP ]
876	Middle of the Linked List	[ Fast-and-slow Pointers ]
875	Koko Eating Bananas	[ Binary Search ]
874	Walking Robot Simulation	[ Solution ]
873	Length of Longest Fibonacci Subsequence	[ DP ]
872	Leaf-Similar Trees	[ DFS ]
871	Minimum Number of Refueling Stops	[ Greedy ]
870	Advantage Shuffle	[ Greedy + Merge-sort ]
869	Reordered Power of 2	[ Solution ]
868	Binary Gap	[ Solution ]
867	Transpose Matrix	[ Solution ]
866	Prime Palindrome	[ Fast Primality Test ]
865	Smallest Subtree with All the Deepest Nodes	[ Tree-DP ]
864	Shortest Path to Get All Keys	[ SPFA ]
863	All Nodes Distance K in Binary Tree	[ DFS ]
862	Shortest Subarray with Sum at Least K	[ Augmented-BST ]
861	Score After Flipping Matrix	[ Greedy+Math ]
860	Lemonade Change	[ Greedy ]
859	Buddy Strings	[ Solution ]
856	Score of Parentheses	[ Divide-and-conquer ]
855	Exam Room	[ TreeSet + PriorityQueue ]
853	Car Fleet	[ Math ]
852	Peak Index in a Mountain Array	[ Binary Search ]
851	Loud and Rich	[ DAG ]
850	Rectangle Area II	[ Rectangle Cutting | Index Compressing ]
849	Maximize Distance to Closest Person	[ Solution ]
848	Shifting Letters	[ Suffix-sum ]
847	Shortest Path Visiting All Nodes	[ Hamiltonian-path ]
846	Hand of Straights	[ Solution ]
845	Longest Mountain in Array	[ Solution ]
844	Backspace String Compare	[ Solution ]
843	Guess the Word	[ Min-max Greedy ]
842	Split Array into Fibonacci Sequence	[ Brute-force ]
841	Keys and Rooms	[ DFS ]
840	Magic Squares in Grid	[ Solution ]
838	Push Dominoes	[ Solution ]
837	Sliding Window	[ DP + Sliding Window ]
836	Rectangle Overlap	[ Solution ]
835	Image Overlap	[ Math ]
834	Sum of Distances in Tree	[ Tree DP ]
833	Find and replace in String	[ Solution ]
832	Flipping an Image	[ Solution ]
831	Masking Personal Information	[ Solution ]
830	Positions of Large Groups	[ Solution ]
829	Consecutive Numbers Sum	[ Math ]
828	Unique Number String	[ Counting ]
827	Making a Large Island	[ Union-Find Set ]
826	Most Profit Assigning Work	[ Greedy | BIT ]
825	Friends of Appropriate Ages	[ Solution ]
824	Goat Latin	[ Solution ]
823	Binary Trees with Factors	[ DP + Two-pointers ]
822	Card Flipping Game	[ Solution ]
821	Shortest Distance to a Character	[ Brute-force | Linear-time Solution ]
820	Short Encoding of Words	[ Greedy ]
815	Bus Routes	[ BFS ]
814	Binary Tree Pruning	[ DFS ]
813	Largest Sum of Averages	[ DP ]
812	Largest Triangle Area	[ Brute-force ]
811	Subdomain Visit Count	[ HashMap ]
810	Chalkboard XOR game	[ Game Theory ]
809	Expressive Words	[ Solution ]
808	Soup Servings	[ DP + Math ]
807	Max Increase to Keep City Skyline	[ Solution ]
806	Number of Lines To Write String	[ Solution ]
805	Split Array with Same Average	[ Pruning + DP | Pruning + DFS ]
804	Unique Morse Code Words	[ Solution ]
799	Champagne Tower	[ Solution ]
798	Smallest Rotation with Highest Score	[ Sliding Window ]
797	All Paths from Source to Target	[ Backtracking ]
796	Rotate String	[ Solution ]
795	Number of Subarrays with Bounded Maximum	[ Divide-and-Conquer | O(n)-time Solution ]
794	Valid Tic-Tac-Toe State	[ Solution ]
793	Preimage Size of Factorial Zeroes Function	[ Binary Search + Math ]
792	Number of Matching Subsequences	[ Linear-time Solution ]
791	Custom Sort String	[ Quick-sort | Counting-sort ]
790	Domino and Tromino Tiling	[ DP ]
789	Escape the Ghosts	[ Math ]
788	Rotated Digits	[ Solution ]
787	Cheapest Flights Within K Stops	[ DP ]
786	K-th Smallest Prime Fraction	[ Partition | Young Tableau ]
785	Is Graph Bipartite?	[ DFS ]
784	Letter Case Permutation	[ Solution ]
783	Minimum Distance Between BST Nodes	[ In-order Traversal ]
781	Rabbits in Forest	[ Math ]
780	Reaching Points	[ Math ]
779	K-th Symbol in Grammar	[ Recursion ]
778	Swim in Rising Water	[ Binary Search + DFS | Dijkstra ]
777	Swap Adjacent in LR String	[ Greedy ]
776	Split BST	[ Recursion ]
775	Global and Local Inversions	[ BIT ]
774	Minimize Max Distance to Gas Station	[ Binary Search ]
773	Sliding Puzzle	[ BFS ]
771	Jewels and Stones	[ Solution ]
769	Max Chunks To Make Sorted	[ Greedy ]
768	Max Chunks To Make Sorted II	[ Greedy | HashMap ]
767	Reorganize String	[ Greedy ]
766	Toeplitz Matrix	[ Solution ]
761	Special Binary String	[ Greedy + Stack ]
760	Find Anagram Mappings	[ Solution ]
759	Employee Free Time	[ Segment Tree ]
758	Bold Words in String	[ Greedy ]
757	Set Intersection Size At Least Two	[ Sweepline + Greedy ]
756	Pyramid Transition Matrix	[ DP ]
755	Pour Water	[ Solution ]
754	Reach a Number	[ Math ]
753	Cracking the Safe	[ Eulerian Circuit ]
752	Open the Lock	[ BFS ]
751	IP to CIDR	[ Greedy + Bit Manipulation ]
750	Number of Corner Rectangles	[ Solution ]
749	Contain Virus	[ DFS ]
748	Shortest Completing Word	[ Solution ]
747	Largest Number Greater Than Twice of Others	[ Solution ]
746	Min Cost Climbing Stairs	[ DP ]
745	Prefix and Suffix Search	[ Solution1 | Solution2 ]
744	Find Smallest Letter Greater Than Target	[ Solution ]
743	Network Delay Time	[ Floyd | SPFA ]
742	Closest Leaf in a Binary Tree	[ DFS ]
741	Cherry Pickup	[ DP ]
740	Delete and Earn	[ DP ]
739	Daily Temperatures	[ Stack ]
738	Monotone Increasing Digits	[ Greedy ]
737	Sentence Similarity II	[ Union-find Set ]
736	Parse Lisp Expression	[ Parser ]
735	Asteroid Collision	[ Stack ]
734	Sentence Similarity	[ Solution ]
733	Flood Fill	[ DFS ]
731	My Calendar II	[ Sweepline | Segment Tree ]
730	Count Different Palindromic Subsequences	[ DP ]
729	My Calendar I	[ Sweepline | Segment Tree ]
728	Self Dividing Numbers	[ Solution ]
727	Minimum Window Subsequence	[ DP ]
726	Number of Atoms	[ LL-Parser | Python Solution | Non-recursive Solution ]
725	Split Linked List in Parts	[ Greedy ]
724	Find Pivot Index	[ Prefix-Sum ]
723	Candy Crush	[ Solution ]
722	Remove Comments	[ Solution ]
721	Accounts Merge	[ Disjoint Set + Hashset ]
720	Longest Word in Dictionary	[ Sorting + DP ]
719	Find K-th Smallest Pair Distance	[ Binary Search + Sliding Window ]
718	Maximum Length of Repeated Subarray	[ DP | Binary Search + Rolling Hash ]
717	1-bit and 2-bit Characters	[ Solution ]
715	Range Module	[ O(n log q)-time Solution via Dynamic Segment Tree ]
714	Best Time to Buy and Sell Stock with Transaction Fee	[ O(n)-time DP ]
713	Subarray Product Less Than K	[ O(n)-time sliding window ]
712	Minimum ASCII Delete Sum for Two Strings	[ DP ]
699	Falling Squares	[ Simple O(n^2)-time Solution | O(n log n)-time Solution via Segment Tree ]
698	Partition to K Equal Sum Subsets	[ Bit-DP ]
697	Degree of an Array	[ HashMap ]
696	Count Binary Substrings	[ DP | Linear Scan ]
695	Max Area of Island	[ DFS ]
694	Number of Distinct Islands	[ DFS + Sorting + Hashing ]
693	Binary Number with Alternating Bits	[ Solution ]
693	Stickers to Spell Word	[ DP + Optimization ]
689	Maximum Sum of 3 Non-overlapping Subarrays	[ DP + Solution Finding ]
688	Knight Probability in Chessboard	[ DP ]
687	Longest Univalue Path	[ Tree-DP ]
686	Repeated String Match	[ Brute-force | KMP ]
685	Redundant Connection II	[ DFS ]
683	K Empty Slots	[ BST ]
682	Baseball Game	[ Implementation ]
681	Next Closest Time	[ Brute-force ]
680	Valid Palindrome II	[ Greedy ]
679	24 Game	[ Backtracking ]
678	Valid Parenthesis String	[ DP ]
677	Map Sum Pairs	[ Trie ]
676	Implement Magic Dictionary	[ Brute-force | Trie + Fuzzy Search ]
675	Cut Off Trees for Golf Event	[ BFS ]
674	Longest Continuous Increasing Subsequence	[ O(n)-time Solution ]
673	Number of Longest Increasing Subsequence	[ O(n^2)-time DP | O(n log n)-time DP via Treap ]
672	Bulb Switcher II	[ Brute-force + Math ]
671	Second Minimum Node in a Binary Tree	[ DFS ]
670	Maximum Swap	[ Brute-force ]
669	Trim a Binary Search Tree	[ DFS ]
668	Kth Smallest Number in Multiplication Table	[ Binary Search ]
667	Beautiful Arrangement II	[ Constructive Approach ]
666	Path Sum IV	[ DFS ]
665	Non-decreasing Array	[ Greedy ]
664	Strange Printer	[ DP ]
663	Equal Tree Partition	[ DFS ]
662	Maximum Width of Binary Tree	[ DFS "Solution" | BFS Solution ]
661	Image Smoother	[ Solution ]
660	Remove 9	[ Base-9 ]
656	Coin Path	[ DP + Printing Solution ]
655	Print Binary Tree	[ DFS + Math ]
654	Maximum Binary Tree	[ DFS ]
653	Two Sum IV - Input is a BST	[ Solution ]
652	Find Duplicate Subtrees	[ Tree-DP | Tree Encoding ]
651	4 Keys Keyboard	[ DP ]
650	2 Keys Keyboard	[ O(n log n)-time DP ]
649	Dota2 Senate	[ Greedy + Queue ]
648	Replace Words	[ Trie ]
647	Palindromic Substrings	[ DP ]
646	Maximum Length of Pair Chain	[ Sweepline ]
645	Set Mismatch	[ Counting Sort ]
644	Maximum Average Subarray II	[ Binary Search + Sliding Window ]
643	Maximum Average Subarray I	[ Sliding Window ]
642	Design Search Autocomplete System	[ Brute-force | Trie ]
640	Solve the Equation	[ Parser ]
639	Decode Ways II	[ Counting ]
638	Shopping Offers	[ DP | Search + Pruning ]
637	Average of Levels in Binary Tree	[ DFS ]
636	Exclusive Time of Functions	[ Stack ]
635	Design Log Storage System	[ Brute-force + Lexicographical Order ]
634	Find the Derangement of an Array	[ Combinatorics ]
633	Sum of Square Numbers	[ Solution | Another Solution ]
632	Smallest Range	[ Greedy + BST ]
631	Design Excel Sum Formula	[ DAG + Implementation ]
630	Course Schedule III	[ Sweep Line + Greedy ]
629	K Inverse Pairs Array	[ Counting ]
628	Maximum Product of Three Numbers	[ Math ]
625	Minimum Factorization	[ Greedy | DP ]
624	Maximum Distance in Arrays	[ Solution ]
623	Add One Row to Tree	[ DFS ]
621	Task Scheduler	[ Simulation + Greedy ]
617	Merge Two Binary Trees	[ DFS ]
616	Add Bold Tag in String	[ O(1000^2)-time Solution ]
611	Valid Triangle Number	[ Three-sum ]
609	Find Duplicate File in System	[ Solution ]
606	Construct String from Binary Tree	[ DFS ]
605	Can Place Flowers	[ Greedy ]
604	Design Compressed String Iterator	[ Lazy Solution ]
600	Non-negative Integers without Consecutive Ones	[ Counting | Digit-DP ]
599	Minimum Index Sum of Two Lists	[ Brute-force ]
598	Range Addition II	[ Solution ]
594	Longest Harmonious Subsequence	[ Brute-force ]
593	Valid Square	[ Elegant Solution ]
592	Fraction Addition and Subtraction	[ Solution ]
591	Tag Validator	[ Recursive Solution ]
588	Design In-memory File System	[ Trie ]
583	Delete Operation for Two Strings	[ LCS ]
582	Kill Process	[ Tree Traversal | Union-find-set-like Solution ]
581	Shortest Unsorted Continuous Subarray	[ Sorting ]
576	Out of Boundary Paths	[ DP ]
575	Distribute Candies	[ Greedy ]
573	Squirrel Simulation	[ Greedy ]
572	Subtree of Another Tree	[ O(n^2)-time Brute-force | O(n)-time Solution | Tree Encoding ]
568	Maximum Vacation Days	[ DP ]
567	Permutation in String	[ Sliding-window ]
566	Reshape the Matrix	[ Brute-force ]
565	Array Nesting	[ Solution ]
564	Find the Closest Palindrome	[ Greedy ]
563	Binary Tree Tilt	[ DFS ]
562	Longest Line of Consecutive One in Matrix	[ Brute-force ]
561	Array Partition I	[ Greedy ]
560	Subarray Sum Equals K	[ Prefix-sum ]
555	Split Assembled Strings	[ Brute-force ]
553	Optimal Division	[ Greedy ]
552	Student Attendance Record II	[ Counting | More Elegant Solution | O(log n)-time Solution | O(log n)-time Solution with Shorter Code ]
551	Student Attendance Record I	[ 1-Liner ]
546	Remove Boxes	[ O(n^4)-time DP ]
545	Boundary of Binary Tree	[ (Careful) Tree Traversal ]
544	Output Contest Matches	[ Brute-force | O(n)-time Solution ]
543	Diameter of Binary Tree	[ DP ]
542	01 Matrix	[ BFS ]
541	Reverse String II	[ Brute-force ]
540	Single Element in a Sorted Array	[ Binary Search ]
539	Minimum Time Difference	[ Sorting ]
538	Convert BST to Greater Tree	[ Right-root-left-traversal ]
537	Complex Number Multiplication	[ Brute-force ]
536	Construct Binary Tree from String	[ LL(1)-parser ]
533	Lonely Pixel II	[ Solution ]
532	K-diff Pairs in an Array	[ O(n)-time Solution | Two-pointer ]
531	Lonely Pixel I	[ Brute-force ]
530	Minimum Absolute Difference in BST	[ DFS ]
529	Minesweeper	[ DFS ]
527	Word Abbreviation	[ Brute-force ]
526	Beautiful Arrangement	[ Permutation ]
525	Contiguous Array	[ Prefix Sum | Divide-and-conquer ]
524	Longest Word in Dictionary through Deleting	[ Greedy ]
523	Continuous Subarray Sum	[ Prefix Sum ]
520	Detect Capital	[ Regex ]
517	Super Washing Machines	[ O(n)-time Solution ]
515	Find Largest Value in Each Tree Row	[ DFS ]
514	Freedom Trail	[ DP | Faster DP ]
513	Find Bottom Left Tree Value	[ DFS ]
509	Most Frequent Subtree Sum	[ Tree Traversal ]
507	Perfect Number	[ O(sqrt(n))-time Solution ]
506	Relative Ranks	[ Sorting ]
505	The Maze II	[ DFS + Pruning | A* Search | DFS + Multithreading ]
504	Base 7	[ 1-line Solution | Conventional Method ]
503	Next Greater Element II	[ Monotone Stack ]
502	IPO	[ Greedy ]
501	Find Mode in Binary Tree	[ DFS + HashMap | O(1)-extra-space Solution ]
500	Keyboard Row	[ 1-Line Solution ]
499	The Maze III	[ A* | DFS ]
498	Diagonal Traversal	[ Sorting | Direct Approach ]
496	Next Greater Element I	[ Brute-force ]
495	Teemo Attacking	[ Sweepline ]
494	Target Sum	[ Knapsack ]
493	Reverse Pairs	[ Merge-sort | Merge-sort Shorter Code | BIT ]
492	Construct the Rectangle	[ Brute-force ]
491	Increasing Subsequences	[ Brute-force ]
490	The Maze	[ DFS ]
488	Zuma Game	[ BFS ]
487	Max Consecutive Ones II	[ O(1)-space Solution ]
486	Predict the Winner	[ DP + Game Theory | Shorter Code ]
485	Max Consecutive Ones	[ Brute-force ]
484	Find Permutation	[ Topological-sort | Constructive Approach ]
483	Smallest Good Base	[ Brute-force + Binary Search ]
482	License Key Formatting	[ Short Solution ]
481	Magical String	[ BFS ]
480	Sliding Window Median	[ Order Statistic Tree via Fenwick Tree ]
477	Total Hamming Distance	[ Bit-by-bit Counting ]
476	Number Complement	[ One-line Solution ]
475	Heaters	[ Direct Approach | Binary Search ]
474	One and Zeroes	[ 0/1-Knapsack ]
473	Matchsticks to Square	[ Backtracking ]
472	Concatenated Words	[ DP + Trie ]
471	Encode String with Shortest Length	[ DP ]
469	Convex Polygon	[ Cross Product ]
468	Validate IP Address	[ Solution ]
467	Unique Substring in Wraparound String	[ String Breaking and Encoding ]
466	Count the Repetitions	[ DP ]
465	Optimal Account Balancing	[ Subset-Sum ]
464	Can I Win	[ DP + Game Theory ]
463	Island Perimeter	[ Brute-force ]
462	Minimum Moves to Equal Array Elements II	[ Median Finding + Quick-Selection ]
461	Hamming Distance	[ Brute-force ]
459	Repeated Substring Pattern	[ O(n^1.5) Solution | 1-Liner | 1-Liner via Regex | Miller-Rabin | KMP ]
456	123 Pattern	[ O(n log n) Solution via BST ]
455	Assign Cookies	[ Greedy ]
454	4Sum II	[ HashMap ]
453	Minimum Moves to Equal Array Elements	[ Solution ]
452	Minimum Number of Arrows to Burst Balloons	[ Greedy via Sweepline ]
451	Sort Characters by Frequency	[ Counting-sort ]
450	Delete Node in a BST	[ Iterative Solution | Shorter Solution ]
449	Serialize and Deserialize BST	[ Pre-order Traversal | Optimized Version ]
448	Find All Numbers Disappeared in an Array	[ Cycle-finding ]
447	Number of Boomerangs	[ Counting via HashMap ]
446	Arithmetic Slices II - Subsequence	[ Very Fast O(n^3) DP Solution | O(n^2) DP Solution with Pruning ]
444	Sequence Reconstruction	[ Topological Sort ]
443	String Compression	[ Solution ]
442	Find All Duplicates in an Array	[ Mod Trick ]
441	Arranging Coins	[ O(1) Brute-force ]
440	K-th Smallest in Lexicographical Order	[ Counting + Greedy ]
439	Ternary Expression Parser	[ Top-down Approach ]
438	Find All Anagrams in a String	[ Sliding-window ]
437	Path Sum III	[ One-pass DFS | One-pass DFS Version 2 | Two-pass DFS ]
436	Find Right Interval	[ TreeMap ]
435	Non-overlapping Intervals	[ Greedy | Activity Selection ]
435	Number of Segments in a String	[ Regex ]
433	Minimum Genetic Mutation	[ BFS ]
432	All O`one Data Structure	[ HashMap + Doubly Circular Linked List ]
425	Word Squares	[ Backtracking + Pruning with Prefix Structure | Hueristic Backtracking + Pruning with BitSet ]
424	Longest Repeating Character Replacement	[ Binary Search | Sliding-window ]
423	Reconstruct Original Digits from English	[ Greedy ]
422	Valid World Square	[ Brute-force ]
421	Maximum XOR of Two Numbers in an Array	[ Binary Trie ]
420	Strong Password Checker	[ Stupid Solution ]
419	Battleships in a Board	[ Single-pass + In-place + No modification ]
418	Sentence Screen Fitting	[ Simulation ]
417	Pacific Atlantic Water Flow	[ Graph Reachability | DP + Vertex Contraction ]
416	Partition Equal Subset Sum	[ 0/1-Knapsack ]
415	Add Strings	[ BigInteger Addition ]
414	Third Maximum Number	[ One-pass Solution ]
413	Arithmetic Slices	[ Solution | In-place Solution ]
412	Fizz Buzz	[ Brute-force ]
411	Minimum Unique Word Abbreviation	[ Brute-force + Pruning ]
410	Split Array Largest Sum	[ Bisect + Greedy ]
409	Longest Palindrome	[ Counting ]
408	Valid Word Abbreviation	[ Brute-force ]
407	Trapping Rain Water II	[ Priority Queue | Dijkstra | SPFA ]
406	Queue Reconstruction by Height	[ Greedy + Sorting ]
405	Convert a Number to Hexadecimal	[ Bit Manipulation ]
404	Sum of Left Leaves	[ DFS ]
403	Frog Jump	[ DP ]
402	Remove K Digits	[ Greedy + Monotone Stack ]
401	Binary Watch	[ Brute-force 1 | Brute-force 2]
400	Nth Digit	[ Counting + Bisect ]
399	Evaluate Division	[ Floyed | DFS ]
398	Random Pick Index	[ Solution1 | Solution2 | Solution3 ]
397	Integer Replacement	[ BFS ]
396	Rotate Fucntion	[ Solution ]
395	Longest Substring with At Least K Repeating Characters	[ O(256N) Solution | Solution with Pruning ]
394	Decode String	[ Top-down Approach ]
393	UTF-8 Validation	[ Solution ]
392	Is Subsequence	[ Solution ]
391	Perfect Rectangle	[ Sweepline + TreeMap | Sweepline + Segment Tree ]
390	Elimination Game	[ O(log n) Math ]
389	Find the Difference	[ Solution ]
388	Longest Absolute File Path	[ Using a Stack | Recursively Solution ]
387	First Unique Character in a String	[ Brute-Force ]
386	Lexicographical Numbers	[ Using a stack | Recursive Solution ]
385	Mini Parser	[ Char-by-char Approach | Using Scanner ]
384	Shuffle an Array	[ Solution ]
383	Ransom Note	[ Solution ]
381	Insert Delete GetRandom O(1) Duplicate Allowed	[ Solution ]
379	Design Phone Directory	[ Simple Solution ]
378	Kth Smallest Element in a Sorted Matrix	[ Bisect + Young Tableau ]
377	Combination Sum IV	[ DP ]
376	Wiggle Subsequence	[ O(n) Climbing Mountain | O(n) In-place Maximal/Minimal Finding ]
375	Guess Number Higher or Lower II	[ O(n^3) DP ]
374	Guess Number Higher or Lower	[ Binary Search ]
373	Find K Pairs with Smallest Sums	[ O(k log k) Solution | O(k log(min(k, m, n)) + min(k, m, n)) Solution ]
372	Super Pow	[ Most-significant Bit -> Least-significant Bit | Least-significant Bit -> Most-significant Bit ]
371	Sum of Two Integers	[ Bit Manipulation ]
370	Range Addition	[ Fenwick Tree | Sweepline | O(n) Prefix Trick | Segment Tree ]
369	Plus One Linked List🔒
368	Largest Divisible Subset	[ DP ]
367	Valid Perfect Square	[ Binary Search ]
366	Find Leaves of Binary Tree	[ Computing Tree Height ]
365	Water and Jug Problem	[ Math ]
364	Nested List Weight Sum II🔒
363	Max Sum of Rectangle No Larger Than K	[ BST ]
362	Design Hit Counter	[ Sliding Window ]
361	Bomb Enemy	[ DP ]
360	Sort Transformed Array	[ O(n)-time Solution ]
359	Logger Rate Limiter	[ Simple Solution | Sliding Window ]
358	Rearrange String k Distance Apart	[ Greedy + Sliding Window ]
357	Count Numbers with Unique Digits	[ Product Rule ]
356	Line Reflection	[ In-place Solution ]
355	Design Twitter	[ k-way Merging ]
354	Russian Doll Envelopes	[ Longest Path | Longest Increasing Subsequence ]
353	Design Snake Game	[ Deque + HashTable ]
352	Data Stream as Disjoint Intervals	[ BST ]
351	Android Unlock Patterns🔒
350	Intersection of Two Arrays II	[ Mergesort ]
349	Intersection of Two Arrays	[ Java Stream ]
348	Design Tic-Tac-Toe	[ O(1)-time Solution ]
347	Top K Frequent Elements	[ Map+QuickSelection | Map+CountingSort ]
346	Moving Average from Data Stream	[ Sliding Window ]
345	Reverse Vowels of a String	[ Two-Pointer ]
344	Reverse String	[ String ]
343	Integer Break	[ Math/DP ]
342	Power of Four	[ Bit Manipulate ]
341	Flatten Nested List Iterator	[ Stack/DFS | Lazier ]
340	Longest Substring with At Most K Distinct Characters	[ O(n) Sliding Window | O(n log n) Bisect | Slinding Window Shorter Code | Sliding Window for Streaming Data (1 pass) ]
339	Nested List Weight Sum	[ DFS ]
338	Counting Bits	[ Counting ]
337	House Robber III	[ Tree DP ]
336	Palindrome Pairs	[ A Naive Solution ]
335	Self Crossing	[ Geometry ]
334	Increasing Triplet Subsequence	[ LIS ]
333	Largest BST Subtree	[ Tree-DP ]
332	Reconstruct Itinerary	[ Euler Path ]
331	Verify Preorder Serialization of a Binary Tree	[ Using a Stack | Property of Full Binary Tree ]
330	Patching Array	[ Greedy Algorithm ]
329	Longest Increasing Path in a Matrix	[ O(nm) DP ]
328	Odd Even Linked List	[ O(n) in-place ]
327	Count of Range Sum	[ O(n log n) solution via Fenwick Tree ]
326	Power of Three	[ An interesting O(log log n) solution ]
325	Maximum Size Subarray Sum Equals k	[ Prefix-sum + HashTable ]
324	Wiggle Sort II	[ Median Finding, Dutch National Flag ]
323	Number of Connected Components in an Undirected Graph	[ DFS ]
322	Coin Change	[ Knapsack ]
321	Create Maximum Number	[ Stack + Greedy ]
320	Generalized Abbreviation	[ Bit-manipulation ]
319	Bulb Switcher	[ O(1) Math ]
318	Maximum Product of Word Lengths	[ O(n^2) brute-force ]
317	Shortest Distance from All Buildings	[ BFS ]
316	Remove Duplicate Letters	[ O(n) Greedy Solution | O(n) Solution via Stack ]
315	Count of Small Numbers After Self	[ Discretization + Fenwick Tree | Mergesort ]
314	Binary Tree Vertical Order TGraversal	[ BFS | BFS (slower, but shorter) ]
313	Super Ugly Number	[ O(nk) Constructive Algorithm ]
312	Burst Balloons	[ O(n^3) DP ]
311	Sparse Matrix Multiplication🔒
310	Minimum Height Trees	[ Longest Path in Tree | Tree DP ]
309	Best Time to Buy and Sell Stock with Cooldown	[ O(n^2) DP | O(n) DP ]
308	Range Sum Query 2D - Mutable	[ 2D-Sqrt Partition | 2D Fenwick Tree ]
307	Range Sum Query - Mutable	[ sqrt(n) Trick | Fenwick Tree | Segment Tree ]
306	Additive Number	[ Fibonacci Sequence ]
305	Number of Islands II	[ Union-Find Set ]
304	Range Sum Query 2D - Immutable	[ Inclusion-Exclusion ]
303	Range Sum Query - Immutable	[ Prefix Sum ]
302	Smallest Rectangle Enclosing Black Pixels	[ DFS ]
301	Remove Invalid Parentheses	[ Backtracking | DP ]
298	Binary Tree Longest Consecutive Sequence	[ Tree-DP | DFS | Another DFS Solution]
297	Serialize and Deserialize Binary Tree	[ DFS ]
294	Flip Game II	[ Nim + Sprague-Grundy Theorem ]
293	Flip Game	[ Brute-force ]
291	Word Pattern II	[ Backtracking | Backtracking + Pruning ]
289	Game of Life	[ In-place Solution | Infinite Board ]
288	Unique Word Abbreviation	[ HashMap ]
286	Walls and Gates	[ BFS]
285	Inorder Successor in BST	[ Top-down Approach | Using Parent Pointers ]
283	Move Zeroes	[ Partition | Cheating ]
281	Zigzag Iterator	[ Solution ]
280	Wiggle Sort	[ One-pass Solution ]
277	Find the Celebrity	[ Universal Sink ]
276	Paint Fence	[ Combinatorial ]
274	H-Index	[ Counting Sort ]
272	Closest Binary Search Tree Value II	[ Predesessor + Successor in BST ]
271	Encode and Decode Strings	[ Escaping Character | Trie Serialization/Deserialization ]
270	Closest Binary Search Tree Value	[ Solution ]
269	Alien Dictionary	[ Topological Sort (BFS) | BFS with Smaller Constant | Topological Sort (DFS)]
267	Palindrome Permutation II	[ Counting + Next Permutation ]
266	Palindrome Permutation	[ Counting ]
265	Paint House II	[ O(nk) DP ]
262	Trips and Users	[ Solution ]
261	Graph Valid Tree	[ Union-find Set ]
259	3Sum Smaller	[ Two-pointer ]
256	Paint House	[ DP ]
255	Verify Preorder Sequence in Binary Search Tree	[ Construction Method | RMQ + Binary Search ]
254	Factor Combinations	[ Backtracking ]
253	Meeting Rooms II	[ Sweepline Algorithm ]
252	Meeting Rooms	[ Sweepline ]
251	Flatten 2D Vector	[ Iterator ]
250	Count Univalue Subtrees	[ DFS ]
249	Group Shifted Strings	[ Keyed-by ]
246	Strobogrammatic Number	[ Brute-force ]
245	Shortest Word Distance III	[ Linear Scan ]
244	Shortest Word Distance II	[ Solution ]
218	The Skyline Problem	[ Sweepline | Java Code]
214	Shortest Palindrome	[ Rabin-Karp rolling hash | KMP ]
212	Word Search II	[ DP + Trie ]
206	Reverse Linked List	[ Solution ]
197	Rising Temperature	[ Solution ]
196	Delete Duplicate Emails	[ Solution ]
186	Reverse Words in a String II	[ In-place Solution ]
184	Department Highest Salary	[ Solution ]
183	Customers Who Never Order	[ Solution ]
182	Duplicate Emails	[ Solution ]
181	Employees Earning More Than Their Managers	[ Solution ]
180	Consecutive Numbers	[ Solution ]
178	Rank Scores	[ Solution ]
177	Nth Highest Salary	[ Solution ]
176	Second Highest Salary	[ Solution ]
175	Combine Two Tables	[ Solution ]
170	Two Sum III - Data structure design	[ Hash Table ]
167	Two Sum II - Input array is sorted	[ Two-pointer ]
165	Compare version Numbers	[ Lexicographical Order ]
163	Missing Ranges	[ Sorting ]
161	One Edit Distance	[ Short Java Code ]
159	Longest Substring with At Most Two Distinct Characters	[ Sliding-window ]
158	Read N Characters Given Read4 II - Call multiple times	[ Reader ]
157	Read N Characters Given Read4	[ Reader ]
156	Binary Tree Upside Down	[ Post-order Traversal ]
155	Min Stack	[ More Memory, Shorter Code | As Little Memory as Possible ]
152	Maximum Product Subarray	[ Three Solutions ]
151	Reverse Words in a String	[ Java Solution | C In-place Solution ]
146	LRU Cache	[ Doubly Connected Linked List + Hash Table ]
140	Word Break II	[ DP + DFS ]
139	Word Break	[ Short DP | DP + Trie ]
136	Single Number	[ Xor | Randomized Partition ]
128	Longest Consecutive Sequence	[ O(n) HashSet ]
127	Word Ladder	[ BFS ]
96	Unique Binary Search Trees	[ DP ]
79	Word Search	[ DFS ]
76	Minimum Window Substring	[ Sliding-window ]
72	Edit Distance	[ DP ]
47	Permutations II	[ next_permutation ]
44	Wildcard Matching	[ DP | Greedy ]
40	Combination Sum II	[ DP Knapsack ]
39	Combination Sum	[ DP + Backtracking ]
37	Sudoku Solver	[ Greedy Backtracking Using Bitmask | Greedy Backtracking ]
36	Valid Sudoku	[ Solution ]
22	Generate Parentheses	[ DP | Recursion ]
10	Regular Expression Matching	[ DP ]
4	Median of Two Sorted Arrays	[ Binary Search ]
2	Add Two Numbers	[ Not in-place | In-place ]
1	Two Sum	[ Two Pointers | Hash Table ]