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
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 ]
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 ]
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🔒
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 ]
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 ]

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