😎
Cracking Leetcode
  • 😎Welcome to TimmyBeef's Cracking Leetcode
  • Recursion tips
  • Atlas
    • 1366. Rank Teams by Votes
  • 3 pointers
    • 689. Maximum Sum of 3 Non-Overlapping Subarrays
  • two pointer
    • Tips
    • 881. Boats to Save People
    • 11. Container With Most Water
    • 27. Remove Element
    • 42. Trapping Rain Water
    • 167. Two Sum II - Input array is sorted
    • 15. 3Sum
    • 611. Valid Triangle Number
    • 18. 4Sum
    • Page 6
    • 344. Reverse String
    • 345. Reverse Vowels of a String
    • 392. Is Subsequence
    • 763. Partition Labels
    • 844. Backspace String Compare
    • 925. Long Pressed Name
    • 977. Squares of a Sorted Array
    • 986. Interval List Intersections
    • Same direction, from start
    • Lintcode - 610. Two Sum - Difference equals to target
    • Lintcode - 1870 · Number of Substrings with All Zeroes
    • 283. Move Zeroes
    • 1513. Number of Substrings With Only 1s
    • 26. Remove Duplicates from Sorted Array
    • sliding win - subarray type
      • 2444. Count Subarrays With Fixed Bounds
      • 992. Subarrays with K Different Integers
      • 2962. Count Subarrays Where Max Element Appears at Least K Times
    • sliding window
      • 395. Longest Substring with At Least K Repeating Characters
      • 1052. Grumpy Bookstore Owner
      • 1208. Get Equal Substrings Within Budget
      • 487. Max Consecutive Ones II
      • lintcode 604 · Window Sum (basic)
      • 3. Longest Substring Without Repeating Characters
      • 340. Longest Substring with At Most K Distinct Characters (sliding window, hashmap, two pointers),
      • 424. Longest Repeating Character Replacement
      • 1151. Minimum Swaps to Group All 1's Together
      • 2134. Minimum Swaps to Group All 1's Together II
      • 1610. Maximum Number of Visible Points
      • 76. Minimum Window Substring (sliding window)
      • 567. Permutation in String
      • 438. Find All Anagrams in a String
      • 1004. Max Consecutive Ones III
      • 1248. Count Number of Nice Subarrays
      • 2516. Take K of Each Character From Left and Right
      • 424. Longest Repeating Character Replacement (ref to 1004
      • Page 12
    • Page 7
    • 1423. Maximum Points You Can Obtain from Cards
    • 643. Maximum Average Subarray I
    • 1176. Diet Plan Performance
    • 125. Valid Palindrome
    • 2108. Find First Palindromic String in the Array
    • 2109. Adding Spaces to a String
    • 2110. Number of Smooth Descent Periods of a Stock
    • 209. Minimum Size Subarray Sum
    • 777. Swap Adjacent in LR String
    • lintcode 1375 · Substring With At Least K Distinct Characters
    • 443. String Compression
    • 1855. Maximum Distance Between a Pair of Values
    • 80. Remove Duplicates from Sorted Array II
    • 26. Remove Duplicates from Sorted Array
    • summaryRanges
    • 5. Longest Palindromic Substring
    • 647. Palindromic Substrings
    • Page 13
  • stack & queue
    • tips
    • 1963. Minimum Number of Swaps to Make the String Balanced
    • 962. Maximum Width Ramp
    • 1249. Minimum Remove to Make Valid Parentheses
    • 232. Implement Queue using Stacks
    • 20. Valid Parentheses
    • 155. Min Stack
    • 394. Decode String
    • 856. Score of Parentheses
    • 224. Basic Calculator
    • 227. Basic Calculator II
    • 946. Validate Stack Sequences
    • 150. Evaluate Reverse Polish Notation
    • 2434. Using a Robot to Print the Lexicographically Smallest String
    • Queue
    • 950. Reveal Cards In Increasing Order
  • Tree
    • N-ary
    • 1261. Find Elements in a Contaminated Binary Tree
    • 2458. Height of Binary Tree After Subtree Removal Queries
    • 2641. Cousins in Binary Tree II
    • 998. Maximum Binary Tree II
    • 1367. Linked List in Binary Tree
    • 1506. Find Root of N-Ary Tree
    • BST
      • 669. Trim a Binary Search Tree
      • 99. Recover Binary Search Tree
      • 501. Find Mode in Binary Search Tree
      • 96. Unique Binary Search Trees
    • Binary Tree classic
      • 333. Largest BST Subtree
      • 965. Univalued Binary Tree
      • 1110. Delete Nodes And Return Forest
      • 450. Delete Node in a BST
      • 1028. Recover a Tree From Preorder Traversal
      • 109. Convert Sorted List to Binary Search Tree
      • 919. Complete Binary Tree Inserter
      • BS DFS enhancement
        • 107. Binary Tree Level Order Traversal II
        • 814. Binary Tree Pruning
        • 979. Distribute Coins in Binary Tree
        • 1325. Delete Leaves With a Given Value
      • 106. Construct Binary Tree from Inorder and Postorder Traversal
      • 105. Construct Binary Tree from Preorder and Inorder Traversal
      • 889. Construct Binary Tree from Preorder and Postorder Traversal
      • 226. Invert Binary Tree
      • 116. Populating Next Right Pointers in Each Node
    • BST classic
      • 1038. Binary Search Tree to Greater Sum Tree
      • 230. Kth Smallest Element in a BST
    • tips
    • 1028. Recover a Tree From Preorder Traversal
    • 971. Flip Binary Tree To Match Preorder Traversal
    • (specail) 314. Binary Tree Vertical Order Traversal
    • (314 followup) 987. Vertical Order Traversal of a Binary Tree
    • 655. Print Binary Tree
    • (bfs)993. Cousins in Binary Tree
    • 94. Binary Tree Inorder Traversal
    • 102. Binary Tree Level Order Traversal (BFS)
    • 114. Flatten Binary Tree to Linked List
    • 144. Binary Tree Preorder Traversal
    • 145. Binary Tree Postorder Traversal
    • preorder
    • 100. Same Tree
    • 101. Symmetric Tree
    • 230. Kth Smallest Element in a BST
    • 257. Binary Tree Paths
    • 112. Path Sum
    • 113. Path Sum II
    • 129. Sum Root to Leaf Numbers (example)
    • 404. Sum of Left Leaves (example)
    • 111. Minimum Depth of Binary Tree
    • 104. Maximum Depth of Binary Tree (divide & conquer)
    • 110. Balanced Binary Tree (divide & conquer)
    • 543. Diameter of Binary Tree
    • 1522. Diameter of N-Ary Tree
    • 687. Longest Univalue Path
    • 515. Find Largest Value in Each Tree Row (BFS)
    • 572. Subtree of Another Tree
    • 589. N-ary Tree Preorder Traversal
    • 590. N-ary Tree Postorder Traversal
    • 617. Merge Two Binary Trees
    • 700. Search in a Binary Search Tree
    • 112. Path Sum
    • 124. Binary Tree Maximum Path Sum
    • 199. Binary Tree Right Side View -BFS
    • 437. Path Sum III
    • 98. Validate Binary Search Tree
    • 270. Closest Binary Search Tree Value
    • 272. Closest Binary Search Tree Value II
    • 173. Binary Search Tree Iterator (stack)
    • 938. Range Sum of BST
    • LCA
      • 235. (LCA) Lowest Common Ancestor of a Binary Search Tree
      • 236. (LCA) Lowest Common Ancestor of a Binary Tree
      • 1644. Lowest Common Ancestor of a Binary Tree II
      • 1650. (LCA) Lowest Common Ancestor of a Binary Tree III
      • 1257. Smallest Common Region
      • 1676. Lowest Common Ancestor of a Binary Tree IV
      • 1123. Lowest Common Ancestor of Deepest Leaves
      • 2096. Step-By-Step Directions From a Binary Tree Node to Another
    • 863. All Nodes Distance K in Binary Tree
    • 652. Find Duplicate Subtrees
    • 366. Find Leaves of Binary Tree
    • 606. Construct String from Binary Tree
    • 285. Inorder Successor in BST
    • 545. Boundary of Binary Tree
    • 582. Kill Process
    • 337. House Robber III
    • 2265. Count Nodes Equal to Average of Subtree
  • DFS & BFS
    • Eulerian paths
      • 332. Reconstruct Itinerary
      • 2097. Valid Arrangement of Pairs
    • Tips
    • Graph I
    • Graph II
      • Bipartite
      • 785. Is Graph Bipartite?
      • 886. Possible Bipartition
      • 1820. Maximum Number of Accepted Invitations (Maximum Bipartite Matching)
      • MST - Prim's Algo
        • 1135. Connecting Cities With Minimum Cost
        • 1584. Min Cost to Connect All Points
      • MST - Kruskal's Algo
        • 1489. Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree
        • 1584. Min Cost to Connect All Points
      • Floyd Algorithm
        • 1334. Find the City With the Smallest Number of Neighbors at a Threshold Distance
    • 988. Smallest String Starting From Leaf
    • 463. Island Perimeter (actually counting
    • 997. Find the Town Judge
    • 1042. Flower Planting With No Adjacent
    • 332. Reconstruct Itinerary
    • Generic DFS
      • 386. Lexicographical Numbers
      • 365. Water and Jug Problem
      • 672. Bulb Switcher II
      • 279. Perfect Squares
      • 37. Sudoku Solver
    • DFS
      • backtracking tips
        • 46. Permutations - example
        • 47. Permutations II (i = 0, sort, used
        • Page 9
        • 39. Combination Sum (not use befroe, so int I = start, dfs(i) -> is i !!
        • 78. Subsets (not use befroe, so int I = start, dfs(i+1)
        • 77. Combinations (not use before, so int I = start, dfs(i+1
        • 90. Subsets II (not use before so int I = start, dfs(i+1), and sort
        • 40. Combination Sum II (not use before so int I = start, dfs(i+1), and sort
        • 17. Letter Combinations of a Phone Number
        • 37. Sudoku Solver
        • 51. N-Queens
        • 60. Permutation Sequence
        • 79. Word Search (backtracking)
        • 212. Word Search II (backtracking)
        • 113. Path Sum II
        • 282. Expression Add Operators
        • 301. Remove Invalid Parentheses
        • 399. Evaluate Division (backtracking
        • 489. Robot Room Cleaner
        • 465. Optimal Account Balancing
        • 996. Number of Squareful Arrays
        • 1568. Minimum Number of Days to Disconnect Island
        • 2065. Maximum Path Quality of a Graph
        • 1306. Jump Game III
        • dispatch to k subsets or ? subsets
          • 473. Matchsticks to Square
          • 698. Partition to K Equal Sum Subsets
          • 1986. Minimum Number of Work Sessions to Finish the Tasks
          • 1723. Find Minimum Time to Finish All Jobs
      • 279. Perfect Squares
      • 241. Different Ways to Add Parentheses
      • 417. Pacific Atlantic Water Flow
      • 200. Number of Islands
      • 959. Regions Cut By Slashes (in the end use 200)
      • 1905. Count Sub Islands
      • 1162. As Far from Land as Possible
      • 1162 compare to 317
      • 22. Generate Parentheses
      • 129. Sum Root to Leaf Numbers
      • 425. Word Squares
      • 694. Number of Distinct Islands
      • 1254. Number of Closed Islands
      • 1020. Number of Enclaves
      • 419. Battleships in a Board
      • 711. Number of Distinct Islands II
      • DFS with return value
      • Copy of 129. Sum Root to Leaf Numbers
      • 2477. Minimum Fuel Cost to Report to the Capital
      • 2492. Minimum Score of a Path Between Two Cities
    • 582. Kill Process
    • BFS
      • 102. Binary Tree Level Order Traversal (BFS)
      • 103. Binary Tree Zigzag Level Order Traversal
      • 127. Word Ladder - BFS
      • 133. Clone Graph (BFS, DFS)
      • 200. Number of Islands (BFS)
      • 733. Flood Fill
      • 1765. Map of Highest Peak
      • 1926. Nearest Exit from Entrance in Maze
      • 317. Shortest Distance from All Buildings
      • 399. Evaluate Division
      • 433. Minimum Genetic Mutation
      • 542. 01 Matrix
      • 547. Number of Provinces
      • 934. Shortest Bridge
      • 994. Rotting Oranges
      • 1091. Shortest Path in Binary Matrix
      • 690. Employee Importance
      • 773. Sliding Puzzle
      • 1293. Shortest Path in a Grid with Obstacles Elimination
      • 818. Race Car
      • Dijkstra
      • 2577. Minimum Time to Visit a Cell In a Grid
      • 01 BFS
        • (01 BFS) 1368. Minimum Cost to Make at Least One Valid Path in a Grid
        • (01 BFS) 2290. Minimum Obstacle Removal to Reach Corner
          • Page 14
      • 2642. Design Graph With Shortest Path Calculator
      • 1514. Path with Maximum Probability (spfa, dijkstra)
      • lintcode 1565 · Modern Ludo I (spfa, dijkstra)
      • 743. Network Delay Time (dijkstra
      • 2662. Minimum Cost of a Path With Special Roads
      • 787. Cheapest Flights Within K Stops (Dijsktra, DP
      • 490. The Maze (spfa
      • 505. The Maze II (spfa
      • 499. The Maze III (spfa, dijkstra
      • 1631. Path With Minimum Effort (dijkstra
      • 752. Open the Lock
      • 1197. Minimum Knight Moves
      • 1730. Shortest Path to Get Food
      • 305. Number of Islands II (union-find)
      • 803. Bricks Falling When Hit (backward union find)
      • 765. Couples Holding Hands
      • 841. Keys and Rooms
      • 2812. Find the Safest Path in a Grid
      • 2510. Check if There is a Path With Equal Number of 0's And 1's
    • 247. Strobogrammatic Number II
  • Binary Search (BS)
    • Template & Tips
    • 2594. Minimum Time to Repair Cars
    • 2226. Maximum Candies Allocated to K Children
    • 274. H-Index
    • 剑指 Offer 53 - II. 0～n-1中缺失的数字
    • 704. Binary Search
    • 33. Search in Rotated Sorted Array
    • 34. Find First and Last Position of Element in Sorted Array
    • 81. Search in Rotated Sorted Array II
    • 35. Search Insert Position
    • 69. Sqrt(x)
    • 74. Search a 2D Matrix
    • 240. Search a 2D Matrix II
    • 278. First Bad Version
    • 349. Intersection of Two Arrays
    • 374. Guess Number Higher or Lower
    • 153. Find Minimum in Rotated Sorted Array
    • 154. Find Minimum in Rotated Sorted Array II
    • 162. Find Peak Element
    • 528. Random Pick with Weight
    • 1428. Leftmost Column with at Least a One
    • 108. Convert Sorted Array to Binary Search Tree
    • 852. Peak Index in a Mountain Array
    • 658. Find K Closest Elements
    • 1891. Cutting Ribbons
    • Lintcode - 610. Two Sum - Difference equals to target
    • State machine or Binary search
      • 792. Number of Matching Subsequences
    • 475. Heaters
    • 410. Split Array Largest Sum
    • 1539. Kth Missing Positive Number
    • 1060. Missing Element in Sorted Array
    • 702. Search in a Sorted Array of Unknown Size
    • 1618. Maximum Font to Fit a Sentence in a Screen
    • New way:
    • 875. Koko Eating Bananas
    • 2517. Maximum Tastiness of Candy Basket ( 類似2616
    • 1011. Capacity To Ship Packages Within D Days
    • 911. Online Election
    • 1482. Minimum Number of Days to Make m Bouquets
    • 1552. Magnetic Force Between Two Balls
  • Greedy
    • 670. Maximum Swap
    • 1605. Find Valid Matrix Given Row and Column Sums
    • 330. Patching Array
    • (same as 330) 2952. Minimum Number of Coins to be Added
    • 1404. Number of Steps to Reduce a Number in Binary Representation to One
    • 55. Jump Game
    • 45. Jump Game II
    • 122. Best Time to Buy and Sell Stock II
    • 134. Gas Station
    • 135. Candy
    • 1840. Maximum Building Height
    • 452. Minimum Number of Arrows to Burst Balloons
    • 455. Assign Cookies
    • 659. Split Array into Consecutive Subsequences
    • 860. Lemonade Change
    • 874. Walking Robot Simulation
    • 1029. Two City Scheduling
    • 1465. Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts
    • 1710. Maximum Units on a Truck
    • 767. Reorganize String
    • lintcode 1871 · Maximum moment
    • 1564. Put Boxes Into the Warehouse I
    • 1580. Put Boxes Into the Warehouse II
    • 921. Minimum Add to Make Parentheses Valid
    • 1167. Minimum Cost to Connect Sticks
    • 871. Minimum Number of Refueling Stops
    • 807. Max Increase to Keep City Skyline
    • 670. Maximum Swap
    • 1675. Minimize Deviation in Array (pq or TreeSet
    • 1567. Maximum Length of Subarray With Positive Product
    • 926. Flip String to Monotone Increasing
    • 2214. Minimum Health to Beat Game
    • 1686. Stone Game VI
  • Divide and Conquer
    • 169. Majority Element
    • 4. Median of Two Sorted Arrays
  • Linked List
    • 2807. Insert Greatest Common Divisors in Linked List
    • 725. Split Linked List in Parts
    • 143. Reorder List
    • 19. Remove Nth Node From End of List
    • 21. Merge Two Sorted Lists
    • 23. Merge k Sorted Lists
    • 141. Linked List Cycle
    • 160. Intersection of Two Linked Lists
    • 206. Reverse Linked List
    • 876. Middle of the Linked List
    • 234. Palindrome Linked List
    • 2816. Double a Number Represented as a Linked List
    • 369. Plus One Linked List
  • Dynamic programming (DP)
    • 1639. Number of Ways to Form a Target String Given a Dictionary
    • Prefix & each position substring
      • 2707. Extra Characters in a String
      • 3291. Minimum Number of Valid Strings to Form Target I
    • 1395. Count Number of Teams
    • 873. Length of Longest Fibonacci Subsequence
    • 741. Cherry Pickup
    • 2222. Number of Ways to Select Buildings
    • 1043. Partition Array for Maximum Sum
    • 1335. Minimum Difficulty of a Job Schedule
    • 2919. Minimum Increment Operations to Make Array
    • 823. Binary Trees With Factors
    • 174. Dungeon Game
    • 396. Rotate Function
    • 467. Unique Substrings in Wraparound String
    • How to save space complexity?
    • tips
    • 509. Fibonacci Number
    • 53. Maximum Subarray (1D-dp)
    • 53. Maximum Subarray (kadane-algo
    • 918. Maximum Sum Circular Subarray (kadane-algo)
    • 2036. Maximum Alternating Subarray Sum (kadane-algo)
    • 152. Maximum Product Subarray (1d-dp)
    • 70. Climbing Stairs (1D-dp)
    • 91. Decode Ways
    • 62. Unique Paths (2D-dp)
    • 63. Unique Paths II (2D-dp)
    • 118. Pascal's Triangle
    • 119. Pascal's Triangle II
    • 2221. Find Triangular Sum of an Array
    • 120. Triangle (1d)
    • 264. Ugly Number II
    • 313. Super Ugly Number
    • LIS
      • 300. Longest Increasing Subsequence (LIS)
      • 354. Russian Doll Envelopes
      • 1964. Find the Longest Valid Obstacle Course at Each Position
      • 673. Number of Longest Increasing Subsequence
      • 2370. Longest Ideal Subsequence
    • 198. House Robber (1d to 2d, 1d, fib)
    • 213. House Robber II
    • 256. Paint House
    • 276. Paint Fence
    • stock tips
      • 121. Best Time to Buy and Sell Stock
      • 122. Best Time to Buy and Sell Stock II
      • 123. Best Time to Buy and Sell Stock III
      • 188. Best Time to Buy and Sell Stock IV
      • 309. Best Time to Buy and Sell Stock with Cooldown
      • 714. Best Time to Buy and Sell Stock with Transaction Fee
    • 1411. Number of Ways to Paint N × 3 Grid
    • 72. Edit Distance
    • 1155. Number of Dice Rolls With Target Sum
    • 區間 dp
      • 132. Palindrome Partitioning II (區間型 + 一般 dp
      • 516. Longest Palindromic Subsequence
    • 322. Coin Change
    • 518. Coin Change 2 (Unbounded Knapsack problem)
    • 01 Knapsack
      • lintcoe 92 · Backpack
      • 416. Partition Equal Subset Sum
      • 474. Ones and Zeroes
      • 1049. Last Stone Weight II
    • Pattern Matching DP
      • 10. Regular Expression Matching
      • 44. Wildcard Matching
      • 97. Interleaving String
      • 718. Maximum Length of Repeated Subarray
      • 1062. Longest Repeating Substring
      • 1143. Longest Common Subsequence
    • math
      • 2485. Find the Pivot Integer
      • 812. Largest Triangle Area
      • Page 2
      • 837. New 21 Game
    • Specail - square DP
      • 221. Maximal Square (2D-dp)
      • 1504. Count Submatrices With All Ones
      • 1277. Count Square Submatrices with All Ones
    • 1048. Longest String Chain
    • 931. Minimum Falling Path Sum
    • 1289. Minimum Falling Path Sum II
    • 1937. Maximum Number of Points with Cost
    • 562. Longest Line of Consecutive One in Matrix (3D DP)
    • 413. Arithmetic Slices
    • 446. Arithmetic Slices II - Subsequence
  • 1218. Longest Arithmetic Subsequence of Given Difference
  • 940. Distinct Subsequences II
  • 552. Student Attendance Record II
  • 664. Strange Printer (區間型 dp
  • 1130. Minimum Cost Tree From Leaf Values (區間型
  • 403. Frog Jump
  • 494. Target Sum
  • (array, can be dp)1014. Best Sightseeing Pair
  • 139. Word Break
  • 140. Word Break II (backtracking)
  • 472. Concatenated Words
  • Page 10
  • 139. Word Break
  • 140. Word Break II
  • 1387. Sort Integers by The Power Value
  • 894. All Possible Full Binary Trees
  • Binary search + Robin karp(rolling hash)
    • 1044. Longest Duplicate Substring
    • 1062. Longest Repeating Substring (bs + rolling hash
  • HashTable, HashMap, HashSet
    • (interesting one) 1002. Find Common Characters
    • 1171. Remove Zero Sum Consecutive Nodes from Linked List
    • 1647. Minimum Deletions to Make Character Frequencies Unique
    • 1481. Least Number of Unique Integers after K Removals
    • Page 8
    • 2131. Longest Palindrome by Concatenating Two Letter Words
    • 1679. Max Number of K-Sum Pairs
    • 1. Two Sum
    • 36. Valid Sudoku
    • 49. Group Anagrams
    • 170. Two Sum III - Data structure design
    • 454. 4Sum II
    • 242. Valid Anagram
    • 243. Shortest Word Distance
    • 244. Shortest Word Distance II
    • 245. Shortest Word Distance III
    • 350. Intersection of Two Arrays II
    • 1160. Find Words That Can Be Formed by Characters
    • 2032. Two Out of Three
    • 981. Time Based Key-Value Store
    • 954. Array of Doubled Pairs
    • 2007. Find Original Array From Doubled Array
    • 811. Subdomain Visit Count
    • 833. Find And Replace in String
    • 1554. Strings Differ by One Character
    • 846. Hand of Straights, 1296. Divide Array in Sets of K Consecutive Numbers
    • 1512. Number of Good Pairs
    • 387. First Unique Character in a String
    • 1010. Pairs of Songs With Total Durations Divisible by 60
    • 1152. Analyze User Website Visit Pattern
    • 1657. Determine if Two Strings Are Close
    • 1347. Minimum Number of Steps to Make Two Strings Anagram
    • 2598. Smallest Missing Non-negative Integer After Operations
  • FB Study way
    • Facebook Tips
  • noname
  • Top K elements (heap, bucket sort)
    • 945. Minimum Increment to Make Array Unique
    • 347. Top K Frequent Elements
    • 692. Top K Frequent Words
    • 451. Sort Characters By Frequency
    • 502. IPO
    • 1046. Last Stone Weight
    • 1851. Minimum Interval to Include Each Query
  • bit
    • 2220. Minimum Bit Flips to Convert Number
    • 2419. Longest Subarray With Maximum Bitwise AND
    • 2917. Find the K-or of an Array
    • 717. 1-bit and 2-bit Characters
    • Xor ^
      • 268. Missing Number
      • 136. Single Number
    • 1310. XOR Queries of a Subarray
    • 371. Sum of Two Integers
    • 2275. Largest Combination With Bitwise AND Greater Than Zero (&1, >>= 1 )
    • Bit Mask
      • 137. Single Number II
      • 320. Generalized Abbreviation
    • 231. Power of Two
    • 191. Number of 1 Bits
    • 461. Hamming Distance
    • 477. Total Hamming Distance
    • Abbreviation
      • 408. Valid Word Abbreviation (two pointers)
    • 1284. Minimum Number of Flips to Convert Binary Matrix to Zero Matrix
    • 389. Find the Difference
  • String problem
    • 3. Longest Substring Without Repeating Characters
    • Perform String Shifts
    • 13. Roman to Integer
    • 14. Longest Common Prefix
    • 38. Count and Say
    • 68. Text Justification
    • 418 Sentence Screen Fitting
    • 151. Reverse Words in a String
    • 592. Fraction Addition and Subtraction
    • Page 1
    • 179. Largest Number
    • 468. Validate IP Address
    • 696. Count Binary Substrings
    • 937. Reorder Data in Log Files
    • 1592. Rearrange Spaces Between Words
    • 949. Largest Time for Given Digits
    • 2047. Number of Valid Words in a Sentence
    • 299. Bulls and Cows
    • 293. Flip Game
    • 1525. Number of Good Ways to Split a String
    • 551. Student Attendance Record I
  • array problem or interval
    • 163. Missing Ranges
    • 1441. Build an Array With Stack Operations
    • 12. Integer to Roman
    • 2373. Largest Local Values in a Matrix
    • 54. Spiral Matrix
    • 59. Spiral Matrix II
    • 2326. Spiral Matrix IV
    • 498. Diagonal Traverse
    • 56. Merge Intervals
    • 57. Insert Interval
    • 31. Next Permutation
    • 556. Next Greater Element III
    • 121. Best Time to Buy and Sell Stock
    • 217. Contains Duplicate
    • 219. Contains Duplicate II
    • 253. Meeting Rooms II
    • (similar to 253 )2406. Divide Intervals Into Minimum Number of Groups
    • lintcode - 1897 · Meeting Room III
    • 2402. Meeting Rooms III
    • 436. Find Right Interval
    • 1272. Remove Interval
    • 1288. Remove Covered Intervals
    • 729. My Calendar I
    • (sort by end)find Max Non-overlapping interval
      • 435. Non-overlapping Intervals
    • 422. Valid Word Square
    • 900. RLE Iterator
    • sweep line
      • 3355. Zero Array Transformation I
      • 3356. Zero Array Transformation II
      • 3346. Maximum Frequency of an Element After Performing Operations I & II
      • 759. Employee Free Time
      • 253. Meeting Rooms II
      • 1094. Car Pooling
      • 56. Merge Interval
      • 729. My Calendar I
      • 731. My Calendar II
      • 732. My Calendar III
    • 2018. Check if Word Can Be Placed In Crossword
    • 2158. Amount of New Area Painted Each Day
    • 2345. Finding the Number of Visible Mountains
  • queue, dqueue
    • mono queue
      • 239. Sliding Window Maximum
      • 1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit
      • 1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit - sliding win +heap
      • 1499. Max Value of Equation
  • stack
    • mono stack
      • 1130. Minimum Cost Tree From Leaf Values
      • 1673. Find the Most Competitive Subsequence
      • Agreegate element on ..range
        • 828. Count Unique Characters of All Substrings of a Given String
      • 1996. The Number of Weak Characters in the Game
      • 739. Daily Temperatures
      • 84. Largest Rectangle in Histogram ( mono increasing stack
      • 456. 132 Pattern
      • 496. Next Greater Element I
      • 503. Next Greater Element II
      • 581. Shortest Unsorted Continuous Subarray
      • 907. Sum of Subarray Minimums
      • 1856. Maximum Subarray Min-Product
      • 2104. Sum of Subarray Ranges
      • 1966. Binary Searchable Numbers in an Unsorted Array
      • 1762. Buildings With an Ocean View
      • 901. Online Stock Span
      • 402. Remove K Digits
      • 316. Remove Duplicate Letters, 1081. Smallest Subsequence of Distinct Characters
      • 255. Verify Preorder Sequence in Binary Search Tree
    • 735. Asteroid Collision
    • 388. Longest Absolute File Path
  • Quick Sort, Quick Select, Kth smallest, Partition
    • tips
    • lintcode 31 · Partition Array (basic)
    • 75. Sort Colors
    • 215. Kth Largest Element in an Array
    • 347. Top K Frequent Elements
    • 973. K Closest Points to Origin
  • Heap
  • 1405. Longest Happy String
  • 1642. Furthest Building You Can Reach
  • Sort
    • 1051. Height Checker
    • 791. Custom Sort String, 1122. Relative Sort Array
    • 853. Car Fleet
    • 1877. Minimize Maximum Pair Sum in Array
    • 1834. Single-Threaded CPU
  • Design
    • 1381. Design a Stack With Increment Operation
    • 146. LRU Cache
    • 295. Find Median from Data Stream
    • 355. Design Twitter
    • 460. LFU Cache
    • 588. Design In-Memory File System
    • 1429. First Unique Number
    • 380. Insert Delete GetRandom O(1)
    • 381. Insert Delete GetRandom O(1) - Duplicates allowed
    • 1146. Snapshot Array
    • 981. Time Based Key-Value Store
    • 359. Logger Rate Limiter
    • 2034. Stock Price Fluctuation
    • 362. Design Hit Counter
    • 348. Design Tic-Tac-Toe
    • 794. Valid Tic-Tac-Toe State
    • 1275. Find Winner on a Tic Tac Toe Game
    • 1628. Design an Expression Tree With Evaluate Function
  • Union Find
    • disjoint set - union find
    • 1579. Remove Max Number of Edges to Keep Graph Fully Traversable
    • 2316. Count Unreachable Pairs of Nodes in an Undirected Graph
    • 261. Graph Valid Tree
    • 323. Number of Connected Components in an Undirected Graph
    • 547. Number of Provinces
    • 990. Satisfiability of Equality Equations
    • 737. Sentence Similarity II (use hashmap version)
    • 684. Redundant Connection
    • 947. Most Stones Removed with Same Row or Column
    • 1202. Smallest String With Swaps
  • Topology sort
    • 207. Course Schedule
    • 210. Course Schedule II
    • 1136. Parallel Courses
    • 2115. Find All Possible Recipes from Given Supplies
    • 269. Alien Dictionary
    • 310. Minimum Height Trees
    • 2285. Maximum Total Importance of Roads
  • merge sort realated
    • 315. Count of Smaller Numbers After Self
  • Path related
    • Dijkstra's Algo
    • 1102. Path With Maximum Minimum Value
  • Couting sort
    • 1122. Relative Sort Array
    • 825. Friends Of Appropriate Ages
  • Trie
    • 208. Implement Trie (Prefix Tree)
    • 211. Design Add and Search Words Data Structure
    • 212. Word Search II
    • 745. Prefix and Suffix Search
    • 1032. Stream of Characters
    • 1268. Search Suggestions System
  • Page 3
  • Math
    • 564. Find the Closest Palindrome
    • 775. Global and Local Inversions
    • 1360. Number of Days Between Two Dates
    • 7. Reverse Integer
    • 9. Palindrome Number
    • 66. Plus One
    • 67. Add Binary
    • 415. Add Strings
    • 2. Add Two Numbers
    • 989. Add to Array-Form of Integer
    • 263. Ugly Number
    • 836. Rectangle Overlap
    • 1025. Divisor Game
    • 202. Happy Number
    • 2033. Minimum Operations to Make a Uni-Value Grid
    • 2048. Next Greater Numerically Balanced Number
    • 843. Guess the Word
    • square
      • 593. Valid Square
      • 939. Minimum Area Rectangle
      • 963. Minimum Area Rectangle II
      • 2013. Detect Squares
    • 384. Shuffle an Array
    • 149. Max Points on a Line
    • 2028. Find Missing Observations
    • 2128. Remove All Ones With Row and Column Flips
    • 539. Minimum Time Difference
    • 258. Add Digits
    • Page 5
    • 957. Prison Cells After N Days
    • 2178. Maximum Split of Positive Even Integers
    • 1492. The kth Factor of n
    • 273. Integer to English Words
  • Prefix Sum
    • 1608. Special Array With X Elements Greater Than or Equal X
    • (prefix product + siliding win)713. Subarray Product Less Than K
    • 930. Binary Subarrays With Sum
    • 2256. Minimum Average Difference
    • Page
    • 303. Range Sum Query - Immutable
    • 304. Range Sum Query 2D - Immutable
    • 560. Subarray Sum Equals K
    • lintcode 1844 · subarray sum equals to k II
    • 325. Maximum Size Subarray Sum Equals k (can refer to lintcode 1844)
    • 209. Minimum Size Subarray Sum
    • 1477. Find Two Non-overlapping Sub-arrays Each With Target Sum
    • 525. Contiguous Array
    • Diff array (差分
      • 370. Range Addition (差分
      • 1109. Corporate Flight Bookings (差分
      • 1094. Car Pooling (差分
      • 995. Minimum Number of K Consecutive Bit Flips
    • 1685. Sum of Absolute Differences in a Sorted Array
    • (sum %= k) 523. Continuous Subarray Sum
    • (sum %= k) 974. Subarray Sums Divisible by K
    • (sum % p) 1590. Make Sum Divisible by P
    • 2845. Count of Interesting Subarrays
    • 2155. All Divisions With the Highest Score of a Binary Array
    • 2875. Minimum Size Subarray in Infinite Array
  • Weekly Contest
    • Weekly Contest 274
      • 2124. Check if All A's Appears Before All B's
      • 2125. Number of Laser Beams in a Bank
      • 2126. Destroying Asteroids
      • 2127. Maximum Employees to Be Invited to a Meeting
    • Weekly Contest 275
      • 2133. Check if Every Row and Column Contains All Numbers
      • 2134. Minimum Swaps to Group All 1's Together II
      • 2135. Count Words Obtained After Adding a Letter
    • Weekly Contest 276
      • 2138. Divide a String Into Groups of Size k
      • 2139. Minimum Moves to Reach Target Score
      • 2140. Solving Questions With Brainpower
      • Page 4
    • Weekly Contest 279
      • 2164. Sort Even and Odd Indices Independently
      • 2165. Smallest Value of the Rearranged Number
      • 2166. Design Bitset
    • Weekly Contest 339
      • 2609. Find the Longest Balanced Substring of a Binary String
      • 2610. Convert an Array Into a 2D Array With Conditions
      • 2611. Mice and Cheese
    • Weekly Contest 340
    • 2614. Prime In Diagonal
    • 2615. Sum of Distances (same as 2121. Intervals Between Identical Elements)
    • 2616. Minimize the Maximum Difference of Pairs (binary search idea
    • TreeMap or TreeSet
    • 432. All O`one Data Structure
    • 2353. Design a Food Rating System
    • 2817. Minimum Absolute Difference Between Elements With Constraint
    • Pratical
    • 2437. Number of Valid Clock Times
    • 681. Next Closest Time
    • Min Max
    • 2905. Find Indices With Index and Value Difference II
    • 2910. Minimum Number of Groups to Create a Valid Assignment
    • Min or Max Prefix Suffix
    • 2012. Sum of Beauty in the Array
    • 2874. Maximum Value of an Ordered Triplet II
    • 2909. Minimum Sum of Mountain Triplets II
    • Greedy
    • 2918. Minimum Equal Sum of Two Arrays After Replacing Zeros
    • 1921. Eliminate Maximum Number of Monsters
    • 2147. Number of Ways to Divide a Long Corridor
    • DFS
    • 814. Binary Tree Pruning
    • 2925. Maximum Score After Applying Operations on a Tree
    • (re-root) 834. Sum of Distances in Tree
    • Math, Geometry
    • 1266. Minimum Time Visiting All Points
    • 2849. Determine if a Cell Is Reachable at a Given Time
    • 1759. Count Number of Homogenous Substrings
    • 2 pointers
    • 1578. Minimum Time to Make Rope Colorful
    • 2332. The Latest Time to Catch a Bus
    • Brainteaser
    • 1503. Last Moment Before All Ants Fall Out of a Plank
    • 1535. Find the Winner of an Array Game
    • Good Qestions
    • 2948. Make Lexicographically Smallest Array by Swapping Elements
    • 1930. Unique Length-3 Palindromic Subsequences
    • 1980. Find Unique Binary String - Cantor's Diagonalization
    • 1727. Largest Submatrix With Rearrangements
    • Backtracking practice
    • 2664. The Knight’s Tour
    • Matrix
    • 1582. Special Positions in a Binary Matrix
    • 531. Lonely Pixel I
  • O(n) to find top2 min or max number
    • 1913. Maximum Product Difference Between Two Pairs
    • 2706. Buy Two Chocolates
    • Some interesting easy
      • 1071. Greatest Common Divisor of Strings
      • 1758. Minimum Changes To Make Alternating Binary String
    • Atlassian
      • 353. Design Snake Game
    • Page 11
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注意: 102, 127 example

qSize 一定要提出來, 不然會錯(why...?
        int qSize = queue.size();
        for (int q = 0; q < qSize; q++) {

https://leetcode.com/problems/binary-tree-postorder-traversal/discuss/45551/Preorder-Inorder-and-Postorder-Iteratively-Summarization
https://cspiration.com/leetcodeClassificationcspiration.com