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Table of Content

Array & String

Array & String

• Sliding Window
  • Fixed Window
    • Naïve Sum/Average
      • Max Sum Subarray of size K (Easy)
      • 643. Maximum Average Subarray I (Easy)
      • 1343. Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold (Medium)
      • 2090. K Radius Subarray Averages (Medium)
      • 1423. Maximum Points You Can Obtain from Cards (Medium)
      • 1176. Diet Plan Performance (Easy)
      • 1052. Grumpy Bookstore Owner (Medium)
      • 1652. Defuse the Bomb (Easy)
    • Hashmap
      • 187. Repeated DNA Sequences (Medium)
    • Hashmap - Duplicate Elements
      • Generic Solution: Find Duplicates within Window Size k
      • 219. Contains Duplicate II (Easy)
      • 217. Contains Duplicate (Easy)
    • Hashmap - Unique/Distinct Elements
      • 1876. Substrings of Size Three with Distinct Characters (Easy)
      • 1852. Distinct Numbers in Each Subarray (Medium)
      • 2107. Number of Unique Flavors After Sharing K Candies (Medium)
      • 1100. Find K-Length Substrings With No Repeated Characters (Medium)
      • Substrings of length k with k-1 distinct elements (Medium)
    • Hashmap - Anagrams/Permutations
      • 438. Find All Anagrams in a String (Medium)
      • 242. Valid Anagram (Easy)
      • 567. Permutation in String (Medium)
    • Count
      • 2379. Minimum Recolors to Get K Consecutive Black Blocks (Easy)
      • 1456. Maximum Number of Vowels in a Substring of Given Length (Medium)
    • Count - Math
      • 1550. Three Consecutive Odds (Easy)
      • 2269. Find the K-Beauty of a Number (Easy)
    • Count - Swaps
      • 1151. Minimum Swaps to Group All 1’s Together (Medium)
      • 2134. Minimum Swaps to Group All 1’s Together II (Medium)
    • Heap
      • 239. Sliding Window Maximum (Hard)
    • Sorting
      • 1984. Minimum Difference Between Highest and Lowest of K Scores (Easy)
    • Bit Manipulation
      • 3023. Find Pattern in Infinite Stream I (Medium)
      • 3037. Find Pattern in Infinite Stream II (Hard)
    • Miscellaneous
      • 30. Substring with Concatenation of All Words (Hard)
  • Longest Sub{string,array}
    • Prospect:
    • Longest Consecutive x with k impurities (1-pass)
      • Generic Solution: Longest Consecutive x with k Impurities (1-pass)
      • 1004. Max Consecutive Ones III (Medium)
      • 487. Max Consecutive Ones II (Medium)
      • 485. Max Consecutive Ones (Easy)
      • 1493. Longest Subarray of 1’s After Deleting One Element (Medium)
    • Longest Consecutive x with k impurities (>1-pass)
      • 1869. Longer Contiguous Segments of Ones than Zeros (Easy)
      • 2024. Maximize the Confusion of an Exam (Medium)
      • 424. Longest Repeating Character Replacement (Medium)
    • Hashmap - Unique Elements
      • 3. Longest Substring Without Repeating Characters (Medium)
      • 1695. Maximum Erasure Value (Medium)
    • Hashmap - K Distinct Elements
      • 340. Longest Substring with At Most K Distinct Characters (Medium)
      • 159. Longest Substring with At Most Two Distinct Characters (Medium)
      • 904. Fruit Into Baskets (Medium)
      • 1446. Consecutive Characters (Easy)
    • Depends on prev
      • 674. Longest Continuous Increasing Subsequence (Easy)
      • 1839. Longest Substring Of All Vowels in Order (Medium)
    • Miscellaneous
      • 1208. Get Equal Substrings Within Budget (Medium)
      • 1658. Minimum Operations to Reduce X to Zero (Medium)
      • 978. Longest Turbulent Subarray (Medium)
      • 2401. Longest Nice Subarray (Medium)
  • Shortest Sub{string,array}
    • Naïve
      • 209. Minimum Size Subarray Sum (Medium)
      • 2260. Minimum Consecutive Cards to Pick Up (Medium)
    • Two strings
      • 76. Minimum Window Substring (Hard)
      • Smallest window containing 0, 1 and 2 (Easy)
  • Return Count,Indices
    • Prospect
    • Naive Sum/Average
      • Indexes of Subarray Sum (Medium)
    • Longest Substring | Depends on prev
      • 1759. Count Number of Homogenous Substrings (Medium)
      • 1513. Number of Substrings With Only 1s (Medium)
    • Less Than K (using atMost)
      • 713. Subarray Product Less Than K (Medium)
      • 2302. Count Subarrays With Score Less Than K (Hard)
    • Exactly K (using atMost)
      • 1248. Count Number of Nice Subarrays (Medium)
      • 992. Subarrays with K Different Integers (Hard)
      • 930. Binary Subarrays With Sum (Medium)
      • 1358. Number of Substrings Containing All Three Characters (Medium)
      • 2799. Count Complete Subarrays in an Array (Medium)
      • 2743. Count Substrings Without Repeating Character (Medium)
    • Exactly K (without atMost)
      • 2537. Count the Number of Good Subarrays (Medium)
      • 2962. Count Subarrays Where Max Element Appears at Least K Times (Medium)
  • TODO’s
  • Tips
  • Visualize me!
• One Pass
  • Math
    • 268. Missing Number (Easy)
  • Uncategorized
    • Second Largest (Easy)
    • 1796. Second Largest Digit in a String (Easy)
    • 2259. Remove Digit From Number to Maximize Result (Easy)
• Two Pointers
  • Read Write Heads
    • Remove Elements
      • 27. Remove Element (Easy)
      • 283. Move Zeroes (Easy)
      • 1119. Remove Vowels from a String (Easy)
    • Remove Elements from Sorted Array
      • Generic - Max frequency is k
      • 80. Remove Duplicates from Sorted Array II (Medium)
      • 26. Remove Duplicates from Sorted Array (Easy)
    • Sort the Array
      • 922. Sort Array By Parity II (Easy)
  • Left Right Heads
    • Classic
      • 125. Valid Palindrome (Easy)
    • Reverse a subarray
      • Generic - Reverse of subarray
      • 344. Reverse String (Easy)
      • 541. Reverse String II (Easy)
      • 2000. Reverse Prefix of Word (Easy)
      • 151. Reverse Words in a String (Medium)
      • 186. Reverse Words in a String II (Medium)
      • 557. Reverse Words in a String III (Easy)
    • Reverse Individual Elements
      • 345. Reverse Vowels of a String (Easy)
      • 917. Reverse Only Letters (Easy)
    • Rotate - Using Reverse
      • 189. Rotate Array (Medium)
      • Quick Left Rotation (Basic)
    • Sorted Array
      • 167. Two Sum II - Input Array Is Sorted (Medium)
    • Sort The Array
      • 977. Squares of a Sorted Array (Easy)
      • 905. Sort Array By Parity (Easy)
  • 2 Heads for 2 Arrays
    • 3 while’s
      • 88. Merge Sorted Array (Easy)
      • 1768. Merge Strings Alternately (Easy)
      • 165. Compare Version Numbers (Medium)
    • Miscellaneous
      • 392. Is Subsequence (Easy)
      • 844. Backspace String Compare (Easy)

Linked List

Linked List

• Singly Linked List
  • Basics
    • Design
      • 707. Design Linked List (Medium)
    • One pointer
    • Two pointer
      • 141. Linked List Cycle (Easy)
      • 142. Linked List Cycle II (Medium)
• Doubly Linked List
  • Basics
    • Design

Search & Sort

Search & Sort

• Binary Search
  • O(logN) , O(sort)
    • The Classic Binary Search Algorithm
      • 704. Binary Search (Easy)
      • 702. Search in a Sorted Array of Unknown Size (Medium)
      • 74. Search a 2D Matrix (Medium)
    • Bisect Algorithms
      • Bisect Left
      • Bisect Left Reverse (with descending elements)
      • Bisect Right
      • Bisect Right Reverse (with descending elements)
    • Bisect Derivatives
      • 744. Find Smallest Letter Greater Than Target (Easy)
      • 35. Search Insert Position (Easy)
      • 362. Design Hit Counter (Medium)
    • Bisect left & right
      • 34. Find First and Last Position of Element in Sorted Array (Medium)
      • 2089. Find Target Indices After Sorting Array (Easy)
      • 1150. Check If a Number Is Majority Element in a Sorted Array (Easy)
      • Element Occurrence (E)
    • Slight Variants
      • 1064. Fixed Point (Easy)
      • 374. Guess Number Higher or Lower (Easy)
      • 278. First Bad Version (Easy)
      • 441. Arranging Coins (Easy)
      • 287. Find the Duplicate Number (Medium)
      • Single Element in a Sorted Array (M)
    • Math - Square
      • 69. Sqrt(x) (Easy)
      • 367. Valid Perfect Square (Easy)
      • 633. Sum of Square Numbers (Medium)
    • Missing Elements
      • 268. Missing Number (Easy)
      • 1060. Missing Element in Sorted Array (Medium)
      • 1539. Kth Missing Positive Number (Easy)
    • Rotated Sorted Array
      • Find the pivot (M)
      • 154. Find Minimum in Rotated Sorted Array II (Hard)
      • 153. Find Minimum in Rotated Sorted Array (Medium)
      • 81. Search in Rotated Sorted Array II (Medium) TODO
      • 33. Search in Rotated Sorted Array (Medium)
    • Peaks in an Array
      • 162. Find Peak Element (Medium)
      • 852. Peak Index in a Mountain Array (Medium)
      • 1095. Find in Mountain Array (Hard)
    • H Index
      • 275. H-Index II (Medium)
      • 274. H-Index (Medium)
  • Secondary loop BS
    • Bisect derivatives
      • 167. Two Sum II - Input Array Is Sorted (Medium)
      • 1855. Maximum Distance Between a Pair of Values (Medium)
      • 1346. Check If N and Its Double Exist (Easy)
    • Bisect derivatives in 2D Matrix
      • 1351. Count Negative Numbers in a Sorted Matrix (Easy)
      • 1337. The K Weakest Rows in a Matrix (Easy)
    • Intersection
      • 349. Intersection of Two Arrays (Easy)
      • 350. Intersection of Two Arrays II (Easy)
      • 1198. Find Smallest Common Element in All Rows (Medium)
      • 1213. Intersection of Three Sorted Arrays (Easy)
    • Custom Bisect
      • 1428. Leftmost Column with at Least a One (Medium)
  • Monotone Function, O(NlogN)
    • Split Input Array
      • 1011. Capacity To Ship Packages Within D Days (Medium)
      • 410. Split Array Largest Sum (Hard)
      • 875. Koko Eating Bananas (Medium)
      • 1482. Minimum Number of Days to Make m Bouquets (Medium)
      • 1231. Divide Chocolate (Hard)
      • 774. Minimize Max Distance to Gas Station (Hard)
      • 1891. Cutting Ribbons (Medium)
      • 2226. Maximum Candies Allocated to K Children (Medium)
      • 2064. Minimized Maximum of Products Distributed to Any Store (Medium)
      • https://leetcode.com/problems/minimized-maximum-of-products-distributed-to-any-store/discuss/1563739/JavaC%2B%2BPython-Binary-Search
      • 2137. Pour Water Between Buckets to Make Water Levels Equal (Medium)
      • 2387. Median of a Row Wise Sorted Matrix (Medium)
    • Kth Smallest
      • 668. Kth Smallest Number in Multiplication Table (Hard)
      • 1918. Kth Smallest Subarray Sum (Medium)

Tree

Tree

• Binary Tree
  • All Traversal
    • Depth First Search
      • 144. Binary Tree Preorder Traversal (Easy)
      • 94. Binary Tree Inorder Traversal (Easy)
      • 145. Binary Tree Postorder Traversal (Easy)
    • Breadth First Search / Level Order
      • 102. Binary Tree Level Order Traversal (Medium)
      • 107. Binary Tree Level Order Traversal II (Medium)
      • 103. Binary Tree Zigzag Level Order Traversal (Medium)
    • Vertical Order
      • 987. Vertical Order Traversal of a Binary Tree (Hard)
      • 314. Binary Tree Vertical Order Traversal (Medium)
  • Level, Height, Depth
    • Depth
      • 104. Maximum Depth of Binary Tree (Easy)
    • Height
      • Tree: Height of a Binary Tree (E)
    • Level
      • 637. Average of Levels in Binary Tree (Easy)
      • 1302. Deepest Leaves Sum (Medium)
      • 513. Find Bottom Left Tree Value (Medium)
      • 1609. Even Odd Tree (Medium)
    • Categorize
      • 543. Diameter of Binary Tree (Easy)
      • 563. Binary Tree Tilt (Easy)
      • 366. Find Leaves of Binary Tree (Medium)
  • Path
    • Path
      • 112. Path Sum (Easy)
      • 257. Binary Tree Paths (Easy)
      • 113. Path Sum II (Medium)
    • Math in it: Bitwise, Divmod
      • 1457. Pseudo-Palindromic Paths in a Binary Tree (Medium)
      • 1022. Sum of Root To Leaf Binary Numbers (Easy)
      • 129. Sum Root to Leaf Numbers (Medium)
    • Simple Path Tracking
      • 404. Sum of Left Leaves (Easy)
      • 1469. Find All The Lonely Nodes (Easy)
  • Side Views, Two Trees
    • Side Views
      • 545. Boundary of Binary Tree (Medium)
      • 199. Binary Tree Right Side View (Medium)
    • Two Trees
      • 100. Same Tree (Easy)
      • 101. Symmetric Tree (Easy)
      • 1379. Find a Corresponding Node of a Binary Tree in a Clone of That Tree (Easy)
      • 872. Leaf-Similar Trees (Easy)
      • 617. Merge Two Binary Trees (Easy)
  • Recursion with Return
    • Recursion with Return
      • 606. Construct String from Binary Tree (Medium)
      • 508. Most Frequent Subtree Sum (Medium)
      • 226. Invert Binary Tree (Easy)
      • 250. Count Univalue Subtrees (Medium)
      • 1026. Maximum Difference Between Node and Ancestor (Medium)
  • Manipulate Tree
    • Create a new tree
      • 654. Maximum Binary Tree (Medium)
  • Print Values of Nodes
• N-ary Tree
  • All Traversals
    • Depth First Search
      • 589. N-ary Tree Preorder Traversal (Easy)
      • 590. N-ary Tree Postorder Traversal (Easy)
    • Breadth First Search / Level Order
      • 429. N-ary Tree Level Order Traversal (Medium)
• Binary Search Tree
  • Manipulate Tree
    • Create
      • 1008. Construct Binary Search Tree from Preorder Traversal (Medium)
    • Convert
      • 897. Increasing Order Search Tree (Easy)
  • All Traversals
    • Traversal
      • 285. Inorder Successor in BST (Medium)
      • 510. Inorder Successor in BST II (Medium)
      • 938. Range Sum of BST (Easy)

Design & Simulation

Design & Simulation

• Array, Hash
  • General
    • 2043. Simple Bank System (Medium)
    • 1603. Design Parking System (Easy)
    • 1476. Subrectangle Queries (Medium)
    • 1656. Design an Ordered Stream (Easy)

Dynamic Programming

Dynamic Programming

• Fibonacci series
  • (REC: N -> 0) Fibonacci Series Extension
    • 509. Fibonacci Number (Easy)
    • 70. Climbing Stairs (Easy)
    • 1137. N-th Tribonacci Number (Easy)
    • Staircase (E)
    • Number factors (E)
  • (REC: N -> 0) Min/Max
    • 746. Min Cost Climbing Stairs (Easy)
    • Minimum jumps with fee (E)
    • 198. House Robber (Medium)
    • 213. House Robber II (Medium)
  • (REC: 0 -> N) Min/Max
    • Minimum jumps to reach the end (E)
• Longest Subsequence
  • HEADING
    • 300. Longest Increasing Subsequence (Medium)

Maths & Bits

Maths & Bits

• Bit Manipulation
  • Foundational Techniques
    • Negating Bits in a Number
    • Determining if the Least Significant Bit (LSB) is Set (Odd/Even Numbers)
    • Unsetting the Least Significant (Rightmost) Set (1) Bit - Brian Kerninghan’s Algorithm
    • Get/Isolate the Least Significant (Rightmost) Set (1) Bit
    • Reverse Bits of a Given 32 Bits Unsigned Integer
    • Swapping Two Variables
  • Trivial Ops
    • 476. Number Complement (Easy)
    • 1009. Complement of Base 10 Integer (Easy)
    • 190. Reverse Bits (Easy)
    • 1486. XOR Operation in an Array (Easy)
    • 1720. Decode XORed Array (Easy)
    • 2433. Find The Original Array of Prefix Xor (Medium)
    • 1829. Maximum XOR for Each Query (Medium)
    • 2932. Maximum Strong Pair XOR I (Easy)
  • Count 1-Bits
    • 191. Number of 1 Bits (Easy)
    • 2595. Number of Even and Odd Bits (Easy)
    • 2859. Sum of Values at Indices With K Set Bits (Easy)
    • 1356. Sort Integers by The Number of 1 Bits (Easy)
    • 2657. Find the Prefix Common Array of Two Arrays (Medium)
    • 461. Hamming Distance (Easy)
    • 2220. Minimum Bit Flips to Convert Number (Easy)
    • 2997. Minimum Number of Operations to Make Array XOR Equal to K (Medium)
    • 1318. Minimum Flips to Make a OR b Equal to c (Medium)
    • TODO - 477. Total Hamming Distance (Medium)
  • LS 1-Bit
    • 231. Power of Two (Easy)
    • 342. Power of Four (Easy)
  • LSB - Loop
    • 2980. Check if Bitwise OR Has Trailing Zeros (Easy)
    • 868. Binary Gap (Easy)
    • 1342. Number of Steps to Reduce a Number to Zero (Easy)
  • XOR - Cancel Bits
    • 136. Single Number (Easy)
    • 540. Single Element in a Sorted Array (Medium)
    • 268. Missing Number (Easy)
    • 389. Find the Difference (Easy)
  • Bitmask - Palindrome
    • 266. Palindrome Permutation (Easy)
    • 1457. Pseudo-Palindromic Paths in a Binary Tree (Medium)
  • Bitmask - Log2
    • 136. Single Number (Easy)
    • 268. Missing Number (Easy)
    • 389. Find the Difference (Easy)
    • 41. First Missing Positive (Hard)
  • Bitmask
    • 448. Find All Numbers Disappeared in an Array (Easy)
    • 442. Find All Duplicates in an Array (Medium)
    • 2206. Divide Array Into Equal Pairs (Easy)
    • 2869. Minimum Operations to Collect Elements (Easy)
    • 1684. Count the Number of Consistent Strings (Easy)
    • 2351. First Letter to Appear Twice (Easy)
    • 2032. Two Out of Three (Easy)
    • 645. Set Mismatch (Easy)
  • Bit by Bit Loop
    • 137. Single Number II (Medium)
    • 2917. Find the K-or of an Array (Easy)
  • Advanced
    • 693. Binary Number with Alternating Bits (Easy)
    • 1256. Encode Number (Medium)
    • 201. Bitwise AND of Numbers Range (Medium)
    • 2568. Minimum Impossible OR (Medium)
    • 260. Single Number III (Medium)
    • 287. Find the Duplicate Number (Medium)
    • 832. Flipping an Image (Easy)
• Math
  • Trailing zeroes in factorial (Easy)