Complete list of all solved problems across all patterns. Main Notes: README.md
| Total | Easy | Medium | Hard |
|---|---|---|---|
| 398 | 90 | 236 | 72 |
Easy: 9 | Medium: 10 | Hard: 1
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 1 | Pair with Target Sum (2Sum II) | 167 | Two Pointers — Both-ends Sum | 🟢 Easy |
| 2 | Triplet Sum to Zero (3Sum) | 15 | Two Pointers — Both-ends Sum | 🟡 Medium |
| 3 | 3Sum Closest | 16 | Two Pointers — Both-ends Sum | 🟡 Medium |
| 4 | Triplets with Smaller Sum | — | Two Pointers — Both-ends Sum | 🟡 Medium |
| 5 | Quadruple Sum to Target (4Sum) | 18 | Two Pointers — Both-ends Sum | 🟡 Medium |
| 6 | Valid Palindrome | 125 | Two Pointers — Both-ends Palindrome | 🟢 Easy |
| 7 | Reverse Vowels of a String | 345 | Two Pointers — Both-ends Swap | 🟢 Easy |
| 8 | Squares of a Sorted Array | 977 | Two Pointers — Both-ends Fill | 🟢 Easy |
| 9 | Remove Duplicates from Sorted Array | 26 | Two Pointers — Slow/Fast | 🟢 Easy |
| 10 | Rearrange 0s and 1s | — | Two Pointers — Slow/Fast | 🟢 Easy |
| 11 | Comparing Strings with Backspaces | 844 | Two Pointers — Reverse Traversal | 🟡 Medium |
| 12 | Sort Colors (Dutch National Flag) | 75 | Two Pointers — 3-pointer | 🟡 Medium |
| 13 | Merge Sorted Array | 88 | Two Pointers — Two Arrays | 🟢 Easy |
| 14 | Is Subsequence | 392 | Two Pointers — Two Arrays | 🟢 Easy |
| 15 | Subarrays with Product Less than K | 713 | Two Pointers — Window/Count | 🟡 Medium |
| 16 | Minimum Window Sort | 581 | Two Pointers — Both-ends Scan | 🟡 Medium |
| 17 | Remove Palindromic Subsequences | 1332 | Two Pointers — Palindrome Check | 🟢 Easy |
| 18 | Reverse Words in a String | 151 | Two Pointers — Both-ends Swap | 🟡 Medium |
| 19 | Trapping Rain Water | 42 | Two Pointers — Both-ends Water | 🔴 Hard |
| 20 | Container with Most Water | 11 | Two Pointers — Both-ends Area | 🟡 Medium |
Easy: 2 | Medium: 14 | Hard: 5
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 138 | Maximum Sum Subarray of Size K | — | Sliding Window — Fixed | 🟢 Easy |
| 139 | Maximum Average Subarray I | 643 | Sliding Window — Fixed | 🟢 Easy |
| 140 | Permutation in a String | 567 | Sliding Window — Fixed | 🟡 Medium |
| 141 | Find All Anagrams in a String | 438 | Sliding Window — Fixed | 🟡 Medium |
| 142 | Longest Substring Without Repeating | 3 | Sliding Window — Variable Maximize | 🟡 Medium |
| 143 | Longest Substring K Distinct | 340 | Sliding Window — Variable Maximize | 🟡 Medium |
| 144 | Fruits into Baskets | 904 | Sliding Window — Variable Maximize | 🟡 Medium |
| 145 | Longest Repeating Char Replacement | 424 | Sliding Window — Variable Maximize | 🔴 Hard |
| 146 | Max Consecutive Ones III | 1004 | Sliding Window — Variable Maximize | 🟡 Medium |
| 147 | Longest Subarray of 1s (Delete One) | 1493 | Sliding Window — Variable Maximize | 🟡 Medium |
| 148 | Get Equal Substrings Within Budget | 1208 | Sliding Window — Variable Maximize | 🟡 Medium |
| 149 | Minimum Size Subarray Sum | 209 | Sliding Window — Variable Minimize | 🟡 Medium |
| 150 | Minimum Window Substring | 76 | Sliding Window — Variable Minimize | 🔴 Hard |
| 151 | Subarray Product Less Than K | 713 | Sliding Window — Variable Count | 🟡 Medium |
| 152 | Subarrays with K Different Integers | 992 | Sliding Window — At-Most Trick | 🔴 Hard |
| 153 | Binary Subarrays with Sum | 930 | Sliding Window — At-Most Trick | 🟡 Medium |
| 154 | Count Number of Nice Subarrays | 1248 | Sliding Window — At-Most Trick | 🟡 Medium |
| 155 | Substring with Concatenation of Words | 30 | Sliding Window — FAANG Hard | 🔴 Hard |
| 156 | Frequency of Most Frequent Element | 1838 | Sliding Window — FAANG Hard | 🟡 Medium |
| 157 | Maximize the Confusion of an Exam | 2024 | Sliding Window — FAANG Hard | 🟡 Medium |
| 158 | Min Ops to Make Array Continuous | 2009 | Sliding Window — FAANG Hard | 🔴 Hard |
Easy: 6 | Medium: 15 | Hard: 2
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 83 | LinkedList Cycle | 141 | Slow & Fast — Cycle Detection | 🟢 Easy |
| 84 | Start of LinkedList Cycle | 142 | Slow & Fast — Cycle Start | 🟡 Medium |
| 85 | Happy Number | 202 | Slow & Fast — Implicit Cycle | 🟡 Medium |
| 86 | Find the Duplicate Number | 287 | Slow & Fast — Implicit Cycle | 🟡 Medium |
| 87 | Middle of the LinkedList | 876 | Slow & Fast — Find Middle | 🟢 Easy |
| 88 | Palindrome LinkedList | 234 | Slow & Fast — Middle + Reverse | 🟡 Medium |
| 89 | Reorder List | 143 | Slow & Fast — Middle + Reverse + Merge | 🟡 Medium |
| 90 | Cycle in a Circular Array | 457 | Slow & Fast — Implicit Cycle (Array) | 🔴 Hard |
| 91 | Remove Nth Node From End | 19 | Slow & Fast — Gap Technique | 🟡 Medium |
| 92 | Intersection of Two Lists | 160 | Slow & Fast — Redirect Technique | 🟢 Easy |
| 93 | Odd Even Linked List | 328 | Slow & Fast — Pointer Rearrangement | 🟡 Medium |
| 94 | String Compression | 443 | Slow & Fast — Slow Write / Fast Read | 🟡 Medium |
| 95 | Remove Duplicates from Sorted Array | 26 | Slow & Fast — Slow Write / Fast Read | 🟢 Easy |
| 96 | Remove Duplicates from Sorted Array II | 80 | Slow & Fast — Slow Write / Fast Read | 🟡 Medium |
| 97 | Duplicate Zeros | 1089 | Slow & Fast — Slow Write / Fast Read | 🟢 Easy |
| 98 | Rotate List | 61 | Slow & Fast — Rotate / Reconnect | 🟡 Medium |
| 99 | Rotate Array | 189 | Slow & Fast — Rotate / Reconnect | 🟡 Medium |
| 100 | Partition Labels | 763 | Slow & Fast — Two-pointer String | 🟡 Medium |
| 101 | Counting Binary Substrings | 696 | Slow & Fast — Two-pointer String | 🟢 Easy |
| 102 | Last Substring in Lexicographical Order | 1163 | Slow & Fast — Two-pointer String | 🔴 Hard |
| 103 | Sort List | 148 | Slow & Fast — Middle + Merge Sort | 🟡 Medium |
| 104 | Number of Subarrays with Bounded Maximum | 795 | Slow & Fast — Two-pointer Count | 🟡 Medium |
| 105 | K-diff Pairs in an Array | 532 | Slow & Fast — Two-pointer Sorted | 🟡 Medium |
Easy: 3 | Medium: 7 | Hard: 2
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 159 | Maximum Subarray Sum | 53 | Kadane — Classic | 🟢 Easy |
| 160 | Minimum Subarray Sum | — | Kadane — Classic | 🟢 Easy |
| 161 | Maximum Product Subarray | 152 | Kadane — Product | 🟡 Medium |
| 162 | Maximum Sum Circular Subarray | 918 | Kadane — Circular | 🟡 Medium |
| 163 | Best Time to Buy and Sell Stock | 121 | Kadane — Stock | 🟢 Easy |
| 164 | Max Subarray Sum with One Deletion | 1186 | Kadane — With State | 🟡 Medium |
| 165 | Longest Subarray with Positive Sum | — | Kadane — Prefix Sum | 🟡 Medium |
| 166 | Maximum Absolute Sum of Any Subarray | 1749 | Kadane — Dual | 🟡 Medium |
| 167 | House Robber | 198 | Kadane — Non-Adjacent DP | 🟡 Medium |
| 168 | Max Sum Rectangle in 2D Matrix | 363 | Kadane — 2D | 🔴 Hard |
| 169 | Max Sum Submatrix No Larger Than K | 363 | Kadane — 2D + Binary Search | 🔴 Hard |
| 170 | Maximum Alternating Subarray Sum | 2036 | Kadane — Alternating | 🟡 Medium |
Easy: 2 | Medium: 7 | Hard: 3
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 171 | Range Sum Query - Immutable | 303 | Prefix Sum — Basic Prefix Array | 🟢 Easy |
| 172 | Find Pivot Index | 724 | Prefix Sum — Basic Prefix Array | 🟢 Easy |
| 173 | Subarray Sum Equals K | 560 | Prefix Sum — HashMap Count | 🟡 Medium |
| 174 | Contiguous Array | 525 | Prefix Sum — HashMap Remap | 🟡 Medium |
| 175 | Longest Subarray with Sum K | 325 | Prefix Sum — HashMap First-seen | 🟡 Medium |
| 176 | Subarray Sums Divisible by K | 974 | Prefix Sum — Modulo HashMap | 🟡 Medium |
| 177 | Continuous Subarray Sum | 523 | Prefix Sum — Modulo HashMap | 🟡 Medium |
| 178 | Range Sum Query 2D - Immutable | 304 | Prefix Sum — 2D Prefix Array | 🟡 Medium |
| 179 | Max Sum of Rectangle No Larger Than K | 363 | Prefix Sum — 2D Prefix + TreeSet | 🔴 Hard |
| 180 | Shortest Subarray with Sum at Least K | 862 | Prefix Sum — Prefix + Deque | 🔴 Hard |
| 181 | Count of Range Sum | 327 | Prefix Sum — Prefix + Merge Sort | 🔴 Hard |
| 182 | Maximum Product Subarray | 152 | Prefix Sum — Prefix Product | 🟡 Medium |
Easy: 1 | Medium: 8 | Hard: 4
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 183 | Merge Intervals | 56 | Merge Interval — Sort + Scan | 🟡 Medium |
| 184 | Insert Interval | 57 | Merge Interval — 3-Phase Insert | 🟡 Medium |
| 185 | Interval List Intersections | 986 | Merge Interval — Two-pointer | 🟡 Medium |
| 186 | Overlapping Intervals Check | — | Merge Interval — Sort + Adjacent | 🟢 Easy |
| 187 | Minimum Meeting Rooms | 253 | Merge Interval — Min-Heap | 🔴 Hard |
| 188 | Maximum CPU Load | — | Merge Interval — Min-Heap | 🔴 Hard |
| 189 | Task Scheduler | 621 | Merge Interval — Max-Heap + Greedy | 🟡 Medium |
| 190 | Non-overlapping Intervals | 435 | Merge Interval — Greedy Sort End | 🟡 Medium |
| 191 | Min Arrows to Burst Balloons | 452 | Merge Interval — Greedy Sort End | 🟡 Medium |
| 192 | Meeting Scheduler | 1229 | Merge Interval — Two-pointer | 🟡 Medium |
| 193 | Employee Free Time | 759 | Merge Interval — Merge + Gap Scan | 🔴 Hard |
| 194 | Remove Covered Intervals | 1288 | Merge Interval — Sort + maxEnd | 🟡 Medium |
| 195 | Data Stream as Disjoint Intervals | 352 | Merge Interval — TreeMap Merge | 🔴 Hard |
Easy: 8 | Medium: 17 | Hard: 6
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 21 | Next Greater Element I | 496 | Stack — Monotonic | 🟢 Easy |
| 22 | Daily Temperatures | 739 | Stack — Monotonic | 🟡 Medium |
| 23 | Next Greater Element II (Circular) | 503 | Stack — Monotonic | 🟡 Medium |
| 24 | Stock Span Problem | 901 | Stack — Monotonic | 🟡 Medium |
| 25 | Online Stock Span | 901 | Stack — Monotonic Design | 🟡 Medium |
| 26 | Largest Rectangle in Histogram | 84 | Stack — Monotonic | 🔴 Hard |
| 27 | Trapping Rain Water | 42 | Stack — Monotonic | 🔴 Hard |
| 28 | Sum of Subarray Minimums | 907 | Stack — Monotonic | 🟡 Medium |
| 29 | Remove Nodes From Linked List | 2487 | Stack — Monotonic | 🟡 Medium |
| 30 | Valid Parentheses | 20 | Stack — Bracket Match | 🟢 Easy |
| 31 | Minimum Remove to Make Valid | 1249 | Stack — Bracket Match | 🟡 Medium |
| 32 | Longest Valid Parentheses | 32 | Stack — Bracket Match | 🔴 Hard |
| 33 | Score of Parentheses | 856 | Stack — Bracket Score | 🟡 Medium |
| 34 | Remove All Adjacent Duplicates I | 1047 | Stack — Removal | 🟢 Easy |
| 36 | Backspace String Compare | 844 | Stack — Simulation | 🟢 Easy |
| 37 | Removing Stars From a String | 2390 | Stack — Simulation | 🟡 Medium |
| 38 | Remove Duplicate Letters | 316 | Stack — Monotonic + Greedy | 🔴 Hard |
| 39 | Remove K Digits | 402 | Stack — Monotonic + Greedy | 🟡 Medium |
| 40 | Evaluate Reverse Polish Notation | 150 | Stack — Expression | 🟡 Medium |
| 41 | Basic Calculator II | 227 | Stack — Expression | 🟡 Medium |
| 42 | Basic Calculator | 224 | Stack — Expression | 🔴 Hard |
| 43 | Decode String | 394 | Stack — Save/Restore | 🟡 Medium |
| 44 | Simplify Path | 71 | Stack — Simulation | 🟡 Medium |
| 45 | Asteroid Collision | 735 | Stack — Conditional | 🟡 Medium |
| 46 | Baseball Game | 682 | Stack — Simulation | 🟢 Easy |
| 47 | Reverse String Using Stack | — | Stack — Basic | 🟢 Easy |
| 48 | Min Stack | 155 | Stack — Design | 🟡 Medium |
| 49 | Implement Queue Using Stacks | 232 | Stack — Design | 🟢 Easy |
| 50 | Implement Stack Using Queues | 225 | Stack — Design | 🟢 Easy |
| 51 | Design Browser History | 1472 | Stack — Design | 🟡 Medium |
| 52 | Maximum Frequency Stack | 895 | Stack — Design | 🔴 Hard |
Easy: 0 | Medium: 1 | Hard: 0
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 35 | Remove All Adjacent Duplicates II | 1209 | Stack + Count | 🟡 Medium |
Easy: 10 | Medium: 6 | Hard: 0
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 53 | Two Sum | 1 | HashMap — Complement Lookup | 🟢 Easy |
| 54 | Valid Anagram | 242 | HashMap — Frequency Count | 🟢 Easy |
| 55 | First Non-Repeating Character | 387 | HashMap — Frequency Count | 🟢 Easy |
| 56 | Maximum Number of Balloons | 1189 | HashMap — Frequency Count | 🟢 Easy |
| 57 | Longest Palindrome | 409 | HashMap — Frequency Count | 🟢 Easy |
| 58 | Ransom Note | 383 | HashMap — Frequency Count | 🟢 Easy |
| 59 | Subarray Sum Equals K | 560 | HashMap — Prefix Sum | 🟡 Medium |
| 60 | Longest Substring Without Repeating | 3 | HashMap — Index Tracking | 🟡 Medium |
| 61 | Group Anagrams | 49 | HashMap — Grouping | 🟡 Medium |
| 62 | Top K Frequent Elements | 347 | HashMap — Frequency Count | 🟡 Medium |
| 63 | Jewels and Stones | 771 | HashMap — HashSet Lookup | 🟢 Easy |
| 64 | Isomorphic Strings | 205 | HashMap — Two-Map Bidirectional | 🟢 Easy |
| 65 | Word Pattern | 290 | HashMap — Two-Map Bidirectional | 🟢 Easy |
| 66 | Contains Duplicate II | 219 | HashMap — Index Tracking | 🟢 Easy |
| 67 | Longest Consecutive Sequence | 128 | HashMap — HashSet + Sequence | 🟡 Medium |
| 68 | LRU Cache | 146 | HashMap — Design (LinkedHashMap) | 🟡 Medium |
Easy: 3 | Medium: 9 | Hard: 2
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 69 | Reverse a LinkedList | 206 | In-Place Reversal — Full | 🟢 Easy |
| 70 | Reverse a Sub-list | 92 | In-Place Reversal — Partial | 🟡 Medium |
| 71 | Reverse List in Pairs | 24 | In-Place Reversal — K-Group k=2 | 🟡 Medium |
| 72 | Reverse Every K-element Sub-list | 25 | In-Place Reversal — K-Group | 🔴 Hard |
| 73 | Reverse Nodes in Even Length Groups | 2074 | In-Place Reversal — Conditional | 🔴 Hard |
| 74 | Rotate a LinkedList | 61 | In-Place Reversal — Rotation | 🟡 Medium |
| 75 | Reverse Alternate K Elements | — | In-Place Reversal — Alternate K | 🟡 Medium |
| 76 | Palindrome LinkedList | 234 | In-Place Reversal — Tool | 🟢 Easy |
| 77 | Reorder List | 143 | In-Place Reversal — Tool | 🟡 Medium |
| 78 | Sort List | 148 | In-Place Reversal — Merge Sort | 🟡 Medium |
| 79 | Remove Nth Node From End | 19 | In-Place Reversal — Gap Technique | 🟡 Medium |
| 80 | Add Two Numbers | 2 | In-Place Reversal — Simulation | 🟡 Medium |
| 81 | Copy List with Random Pointer | 138 | In-Place Reversal — Clone | 🟡 Medium |
| 82 | Merge Two Sorted Lists | 21 | In-Place Reversal — Merge | 🟢 Easy |
Easy: 6 | Medium: 20 | Hard: 6
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 106 | Binary Search | 704 | Binary Search — Basic | 🟢 Easy |
| 107 | Search Insert Position | 35 | Binary Search — Upper Bound | 🟢 Easy |
| 108 | First and Last Position | 34 | Binary Search — Boundary Search | 🟡 Medium |
| 109 | Count Occurrences in Sorted Array | — | Binary Search — Counting | 🟢 Easy |
| 110 | Search in Infinite Sorted Array | — | Binary Search — Exponential + BS | 🟡 Medium |
| 111 | Peak Index in Mountain Array | 852 | Binary Search — Bitonic | 🟢 Easy |
| 112 | Search in Bitonic Array | — | Binary Search — Bitonic | 🟡 Medium |
| 113 | Find Peak Element | 162 | Binary Search — Bitonic | 🟡 Medium |
| 114 | Find Minimum in Rotated Sorted Array | 153 | Binary Search — Range Search | 🟡 Medium |
| 115 | Find Number of Rotations | — | Binary Search — Range Search | 🟢 Easy |
| 116 | Search in Rotated Sorted Array | 33 | Binary Search — Range Search | 🟡 Medium |
| 117 | Find Min in Rotated II (Duplicates) | 154 | Binary Search — Range Search | 🔴 Hard |
| 118 | Search in Rotated II (Duplicates) | 81 | Binary Search — Range Search | 🟡 Medium |
| 119 | Single Element in Sorted Array | 540 | Binary Search — Parity | 🟡 Medium |
| 120 | Koko Eating Bananas | 875 | Binary Search — Allocate | 🟡 Medium |
| 121 | Min Days to Make M Bouquets | 1482 | Binary Search — Allocate | 🟡 Medium |
| 122 | Aggressive Cows | — | Binary Search — Allocate | 🟡 Medium |
| 123 | H-Index II | 275 | Binary Search — Allocate | 🟡 Medium |
| 124 | Maximum Candies to K Children | 2226 | Binary Search — Allocate | 🟡 Medium |
| 125 | Capacity to Ship in D Days | 1011 | Binary Search — Allocate | 🟡 Medium |
| 126 | Book Allocation Problem | — | Binary Search — Allocate | 🔴 Hard |
| 127 | Split Array Largest Sum | 410 | Binary Search — Allocate | 🔴 Hard |
| 128 | Minimum Speed to Arrive on Time | 1870 | Binary Search — Allocate | 🟡 Medium |
| 129 | Minimize Max Gas Station Distance | 774 | Binary Search — Allocate | 🔴 Hard |
| 130 | Search a 2D Matrix | 74 | Binary Search — 2D | 🟡 Medium |
| 131 | Search a 2D Matrix II | 240 | Binary Search — 2D (Staircase) | 🟡 Medium |
| 132 | Kth Smallest in Sorted Matrix | 378 | Binary Search — Kth Element | 🟡 Medium |
| 133 | Kth Smallest in Multiplication Table | 668 | Binary Search — Kth Element | 🔴 Hard |
| 134 | Median of Two Sorted Arrays | 4 | Binary Search — Partition | 🔴 Hard |
| 135 | Kth Missing Positive Number | 1539 | Binary Search — Missing Count | 🟢 Easy |
| 136 | Time Based Key-Value Store | 981 | Binary Search — FAANG | 🟡 Medium |
| 137 | Find K Closest Elements | 658 | Binary Search — FAANG | 🟡 Medium |
Easy: 7 | Medium: 2 | Hard: 3
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 196 | Cyclic Sort | — | Cyclic Sort — Core | 🟢 Easy |
| 197 | Find the Missing Number | 268 | Cyclic Sort — Missing | 🟢 Easy |
| 198 | Find All Missing Numbers | 448 | Cyclic Sort — All Missing | 🟢 Easy |
| 199 | Find the Duplicate Number | 287 | Cyclic Sort — Duplicate | 🟡 Medium |
| 200 | Find All Duplicate Numbers | 442 | Cyclic Sort — All Duplicates | 🟡 Medium |
| 201 | Find the Corrupt Pair | — | Cyclic Sort — Combined | 🟢 Easy |
| 202 | Smallest Missing Positive Number | 41 | Cyclic Sort — Missing Positive | 🔴 Hard |
| 203 | First K Missing Positive Numbers | — | Cyclic Sort — K Missing | 🔴 Hard |
| 204 | Set Mismatch | 645 | Cyclic Sort — Combined | 🟢 Easy |
| 205 | Find All Numbers Disappeared | 448 | Cyclic Sort — All Missing | 🟢 Easy |
| 206 | First Missing Positive | 41 | Cyclic Sort — Missing Positive | 🔴 Hard |
| 207 | Missing Number (XOR/Math) | 268 | Cyclic Sort — Missing (Multi-approach) | 🟢 Easy |
Easy: 4 | Medium: 14 | Hard: 7
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 208 | Kth Largest Element in an Array | 215 | Heap — Kth Element | 🟡 Medium |
| 209 | Kth Smallest Element in Sorted Matrix | 378 | Heap — Kth Element | 🟡 Medium |
| 210 | Kth Largest Element in a Stream | 703 | Heap — Kth Element Design | 🟢 Easy |
| 211 | Kth Weakest Row in a Matrix | 1337 | Heap — Kth Element | 🟢 Easy |
| 212 | Top K Frequent Elements | 347 | Heap — Top K | 🟡 Medium |
| 213 | Top K Frequent Words | 692 | Heap — Top K | 🟡 Medium |
| 214 | Sort Characters By Frequency | 451 | Heap — Top K | 🟡 Medium |
| 215 | K Closest Points to Origin | 973 | Heap — Top K | 🟡 Medium |
| 216 | Find K Closest Elements | 658 | Heap — Top K | 🟡 Medium |
| 217 | Merge K Sorted Lists | 23 | Heap — Merge K | 🔴 Hard |
| 218 | Merge K Sorted Arrays | — | Heap — Merge K | 🟡 Medium |
| 219 | K Pairs with Smallest Sums | 373 | Heap — Merge K | 🟡 Medium |
| 220 | Smallest Range Covering K Lists | 632 | Heap — Merge K | 🔴 Hard |
| 221 | Find Median from Data Stream | 295 | Heap — Two Heaps | 🔴 Hard |
| 222 | Sliding Window Median | 480 | Heap — Two Heaps | 🔴 Hard |
| 223 | Task Scheduler | 621 | Heap — Greedy | 🟡 Medium |
| 224 | Reorganize String | 767 | Heap — Greedy | 🟡 Medium |
| 225 | Last Stone Weight | 1046 | Heap — Greedy | 🟢 Easy |
| 226 | IPO | 502 | Heap — Greedy | 🔴 Hard |
| 227 | Course Schedule III | 630 | Heap — Greedy | 🔴 Hard |
| 228 | Minimum Number of Refueling Stops | 871 | Heap — Greedy | 🔴 Hard |
| 229 | Design Twitter | 355 | Heap — Design | 🟡 Medium |
| 230 | Design Food Rating System | 2353 | Heap — Design | 🟡 Medium |
| 231 | Distant Barcodes | 1054 | Heap — Greedy | 🟡 Medium |
| 232 | Sort Array by Frequency | 1636 | Heap — Top K | 🟢 Easy |
Easy: 6 | Medium: 4 | Hard: 3
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 287 | Fibonacci Number | 509 | Recursion — Basic | 🟢 Easy |
| 288 | Check if String is Palindrome | — | Recursion — Basic | 🟢 Easy |
| 289 | Check if Array is Sorted | — | Recursion — Basic | 🟢 Easy |
| 290 | Sum of Digits of a Number | — | Recursion — Basic | 🟢 Easy |
| 291 | Remove Occurrences of a Character | — | Recursion — Basic | 🟢 Easy |
| 292 | Count Good Numbers | 1922 | Recursion — Basic | 🟡 Medium |
| 293 | Pow(x, n) | 50 | Recursion — D&C | 🟡 Medium |
| 294 | Binary Search (Recursive) | 704 | Recursion — D&C | 🟢 Easy |
| 295 | Merge Sort | — | Recursion — D&C | 🟡 Medium |
| 296 | Maximum Subarray (D&C) | 53 | Recursion — D&C | 🟡 Medium |
| 297 | Count Smaller Numbers After Self | 315 | Recursion — D&C | 🔴 Hard |
| 298 | Reverse Pairs | 493 | Recursion — D&C | 🔴 Hard |
| 299 | Count of Range Sum | 327 | Recursion — D&C | 🔴 Hard |
Easy: 0 | Medium: 13 | Hard: 3
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 300 | Subsets | 78 | Backtracking — Subsets | 🟡 Medium |
| 301 | Subsets II | 90 | Backtracking — Subsets | 🟡 Medium |
| 302 | Permutations | 46 | Backtracking — Permutations | 🟡 Medium |
| 303 | Permutations II | 47 | Backtracking — Permutations | 🟡 Medium |
| 304 | Combinations | 77 | Backtracking — Combinations | 🟡 Medium |
| 305 | Combination Sum | 39 | Backtracking — Combinations | 🟡 Medium |
| 306 | Combination Sum II | 40 | Backtracking — Combinations | 🟡 Medium |
| 307 | Generate Parentheses | 22 | Backtracking — String | 🟡 Medium |
| 308 | Letter Combinations of a Phone Number | 17 | Backtracking — String | 🟡 Medium |
| 309 | Palindrome Partitioning | 131 | Backtracking — String | 🟡 Medium |
| 310 | Split String | — | Backtracking — String | 🟡 Medium |
| 311 | N-Queens | 51 | Backtracking — Hard | 🔴 Hard |
| 312 | Word Search | 79 | Backtracking — Grid | 🟡 Medium |
| 313 | Sudoku Solver | 37 | Backtracking — Hard | 🔴 Hard |
| 314 | Unique Paths III | 980 | Backtracking — Grid | 🔴 Hard |
| 315 | Path with Maximum Gold | 1219 | Backtracking — Grid | 🟡 Medium |
Easy: 0 | Medium: 1 | Hard: 0
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 316 | Jump Game | 55 | Recursive Search | 🟡 Medium |
Easy: 20 | Medium: 30 | Hard: 4
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 233 | Binary Tree Inorder Traversal | 94 | Tree — Traversal | 🟢 Easy |
| 234 | Binary Tree Preorder Traversal | 144 | Tree — Traversal | 🟢 Easy |
| 235 | Binary Tree Postorder Traversal | 145 | Tree — Traversal | 🟢 Easy |
| 236 | Binary Tree Level Order Traversal | 102 | Tree — BFS | 🟡 Medium |
| 237 | Binary Tree Zigzag Level Order | 103 | Tree — BFS | 🟡 Medium |
| 238 | Binary Tree Level Order Traversal II | 107 | Tree — BFS | 🟢 Easy |
| 239 | Invert Binary Tree | 226 | Tree — Mirror | 🟢 Easy |
| 240 | Symmetric Tree | 101 | Tree — Symmetry | 🟢 Easy |
| 241 | Same Tree | 100 | Tree — Comparison | 🟢 Easy |
| 242 | Subtree of Another Tree | 572 | Tree — Comparison | 🟡 Medium |
| 243 | Flip Equivalent Binary Trees | 951 | Tree — Mirror | 🟡 Medium |
| 244 | Search in a Binary Search Tree | 700 | Tree — BST Search | 🟢 Easy |
| 245 | Lowest Common Ancestor of BST | 235 | Tree — BST LCA | 🟡 Medium |
| 246 | Lowest Common Ancestor of Binary Tree | 236 | Tree — LCA | 🟡 Medium |
| 247 | LCA of Deepest Leaves | 1123 | Tree — LCA | 🟡 Medium |
| 248 | Find Mode in BST | 501 | Tree — BST Traversal | 🟢 Easy |
| 249 | Two Sum IV — BST | 653 | Tree — BST Search | 🟢 Easy |
| 250 | Kth Smallest Element in BST | 230 | Tree — BST Inorder | 🟡 Medium |
| 251 | Minimum Depth of Binary Tree | 111 | Tree — Depth | 🟢 Easy |
| 252 | Maximum Depth of Binary Tree | 104 | Tree — Depth | 🟢 Easy |
| 253 | Balanced Binary Tree | 110 | Tree — Validation | 🟢 Easy |
| 254 | Diameter of Binary Tree | 543 | Tree — Properties | 🟢 Easy |
| 255 | Binary Tree Tilt | 563 | Tree — Properties | 🟢 Easy |
| 256 | Check Completeness of Binary Tree | 958 | Tree — Validation | 🟡 Medium |
| 257 | Validate Binary Search Tree | 98 | Tree — BST Validation | 🟡 Medium |
| 258 | Recover Binary Search Tree | 99 | Tree — BST Recovery | 🔴 Hard |
| 259 | Path Sum | 112 | Tree — Path Sum | 🟢 Easy |
| 260 | Path Sum II | 113 | Tree — Path Sum | 🟡 Medium |
| 261 | Path Sum III | 437 | Tree — Path Sum | 🟡 Medium |
| 262 | Sum Root to Leaf Numbers | 129 | Tree — Path Sum | 🟡 Medium |
| 263 | Binary Tree Maximum Path Sum | 124 | Tree — Path Sum | 🔴 Hard |
| 264 | Construct BT from Preorder and Inorder | 105 | Tree — Construction | 🟡 Medium |
| 265 | Construct BT from Inorder and Postorder | 106 | Tree — Construction | 🟡 Medium |
| 266 | Construct BT from Preorder and Postorder | 889 | Tree — Construction | 🟡 Medium |
| 267 | Convert Sorted Array to BST | 108 | Tree — Construction | 🟢 Easy |
| 268 | Convert Sorted List to BST | 109 | Tree — Construction | 🟡 Medium |
| 269 | Serialize and Deserialize Binary Tree | 297 | Tree — Serialization | 🔴 Hard |
| 270 | Even Odd Tree | 1609 | Tree — BFS | 🟡 Medium |
| 271 | Reverse Odd Levels of Binary Tree | 2415 | Tree — BFS | 🟡 Medium |
| 272 | Deepest Leaves Sum | 1302 | Tree — BFS | 🟡 Medium |
| 273 | Add One Row to Tree | 623 | Tree — BFS | 🟡 Medium |
| 274 | Maximum Width of Binary Tree | 662 | Tree — BFS | 🟡 Medium |
| 275 | All Nodes Distance K in Binary Tree | 863 | Tree — BFS + Graph | 🟡 Medium |
| 276 | Maximum Binary Tree | 654 | Tree — Construction | 🟡 Medium |
| 277 | Construct BST from Preorder Traversal | 1008 | Tree — Construction | 🟡 Medium |
| 278 | Binary Tree Paths | 257 | Tree — Root to Leaf | 🟢 Easy |
| 279 | Smallest String Starting from Leaf | 988 | Tree — Root to Leaf | 🟡 Medium |
| 280 | Insufficient Nodes in Root to Leaf | 1080 | Tree — Root to Leaf | 🟡 Medium |
| 281 | Pseudo-Palindromic Paths in Binary Tree | 1457 | Tree — Root to Leaf | 🟡 Medium |
| 282 | Maximum Difference Between Node and Ancestor | 1026 | Tree — Ancestor | 🟡 Medium |
| 283 | Kth Ancestor of a Tree Node | 1483 | Tree — Ancestor | 🔴 Hard |
| 284 | Range Sum of BST | 938 | Tree — BST | 🟢 Easy |
| 285 | Minimum Absolute Difference in BST | 530 | Tree — BST Inorder | 🟢 Easy |
| 286 | Insert into a BST | 701 | Tree — BST Insert | 🟡 Medium |
Easy: 1 | Medium: 33 | Hard: 10
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 317 | Number of Islands | 200 | Graph — DFS/BFS | 🟡 Medium |
| 318 | Friend Circles (Number of Provinces) | 547 | Graph — DFS/UF | 🟡 Medium |
| 319 | Max Area of Island | 695 | Graph — DFS | 🟡 Medium |
| 320 | Surrounded Regions | 130 | Graph — DFS Boundary | 🟡 Medium |
| 321 | Shortest Path in Binary Matrix | 1091 | Graph — BFS | 🟡 Medium |
| 322 | Word Ladder | 127 | Graph — BFS | 🔴 Hard |
| 323 | Path with Minimum Effort | 1631 | Graph — Dijkstra | 🟡 Medium |
| 324 | Swim in Rising Water | 778 | Graph — Dijkstra | 🔴 Hard |
| 325 | Find Eventual Safe States | 802 | Graph — DFS Cycle | 🟡 Medium |
| 326 | All Paths Source to Target | 797 | Graph — DFS | 🟡 Medium |
| 327 | Longest Increasing Path in Matrix | 329 | Graph — DFS + Memo | 🔴 Hard |
| 328 | Network Delay Time | 743 | Graph — Dijkstra | 🟡 Medium |
| 329 | Cheapest Flights Within K Stops | 787 | Graph — Bellman-Ford | 🟡 Medium |
| 330 | Path with Maximum Probability | 1514 | Graph — Dijkstra | 🟡 Medium |
| 331 | Find the City (Smallest Neighbours) | 1334 | Graph — Floyd-Warshall | 🟡 Medium |
| 332 | Course Schedule | 207 | Graph — Topological Sort | 🟡 Medium |
| 333 | Course Schedule II | 210 | Graph — Topological Sort | 🟡 Medium |
| 334 | Course Schedule IV | 1462 | Graph — Topological Sort | 🟡 Medium |
| 335 | Alien Dictionary | 269 | Graph — Topological Sort | 🔴 Hard |
| 336 | Sequence Reconstruction | 444 | Graph — Topological Sort | 🟡 Medium |
| 337 | Redundant Connection | 684 | Graph — Union Find | 🟡 Medium |
| 338 | Redundant Connection II | 685 | Graph — Union Find | 🔴 Hard |
| 339 | Accounts Merge | 721 | Graph — Union Find | 🟡 Medium |
| 340 | Number of Operations — Network | 1319 | Graph — Union Find | 🟡 Medium |
| 341 | Satisfiability of Equality Equations | 990 | Graph — Union Find | 🟡 Medium |
| 342 | Min Cost to Connect All Points | 1584 | Graph — Kruskal / Prim | 🟡 Medium |
| 343 | Connecting Cities with Min Cost | 1135 | Graph — Kruskal | 🟡 Medium |
| 344 | Is Graph Bipartite? | 785 | Graph — BFS Coloring | 🟡 Medium |
| 345 | Possible Bipartition | 886 | Graph — BFS Coloring | 🟡 Medium |
| 346 | Flower Planting With No Adjacent | 1042 | Graph — Greedy Coloring | 🟢 Easy |
| 347 | M-Coloring Problem | — | Graph — Backtracking | 🟡 Medium |
| 348 | Min Cost to Provide Water | 1168 | Graph — Kruskal | 🔴 Hard |
| 349 | Minimum Obstacle Removal | 2290 | Graph — 0-1 BFS | 🔴 Hard |
| 350 | Minimum Moves to Move Box | 1263 | Graph — BFS (states) | 🔴 Hard |
| 351 | Minimum Cost Reach Destination in Time | 1928 | Graph — Dijkstra | 🔴 Hard |
| 352 | Connect Sticks (Min Cost) | 1167 | Graph — Greedy Heap | 🟡 Medium |
| 353 | Longest Path in DAG | — | Graph — Topo Sort + DP | 🟡 Medium |
| 354 | Number of Enclaves | 1020 | Graph — DFS Boundary | 🟡 Medium |
| 355 | Time to Inform All Employees | 1376 | Graph — DFS | 🟡 Medium |
| 356 | 01 Matrix | 542 | Graph — Multi-source BFS | 🟡 Medium |
| 357 | Rotting Oranges | 994 | Graph — Multi-source BFS | 🟡 Medium |
| 358 | As Far from Land as Possible | 1162 | Graph — Multi-source BFS | 🟡 Medium |
| 359 | Most Stones Removed | 947 | Graph — Union Find | 🟡 Medium |
| 360 | Strange Printer II | 1591 | Graph — Topological Sort | 🔴 Hard |
Easy: 2 | Medium: 25 | Hard: 11
| # | Problem | LC # | Sub-Pattern | Difficulty |
|---|---|---|---|---|
| 361 | House Robber | 198 | DP — Fibonacci / Decision | 🟡 Medium |
| 362 | Maximum Subarray | 53 | DP — Fibonacci / Decision | 🟢 Easy |
| 363 | Decode Ways | 91 | DP — Fibonacci / Decision | 🟡 Medium |
| 364 | Coin Change | 322 | DP — Min/Max Path | 🟡 Medium |
| 365 | Minimum Path Sum | 64 | DP — Min/Max Path | 🟡 Medium |
| 366 | Minimum Falling Path Sum | 931 | DP — Min/Max Path | 🟡 Medium |
| 367 | Unique Paths | 62 | DP — Min/Max Path | 🟡 Medium |
| 368 | 0/1 Knapsack | — | DP — 0/1 Knapsack | 🟡 Medium |
| 369 | Partition Equal Subset Sum | 416 | DP — 0/1 Knapsack | 🟡 Medium |
| 370 | Target Sum | 494 | DP — 0/1 Knapsack | 🟡 Medium |
| 371 | Ones and Zeroes | 474 | DP — 0/1 Knapsack | 🟡 Medium |
| 372 | Last Stone Weight II | 1049 | DP — 0/1 Knapsack | 🟡 Medium |
| 373 | Coin Change II | 518 | DP — Unbounded Knapsack | 🟡 Medium |
| 374 | Count Numbers with Unique Digits | 357 | DP — Unbounded Knapsack | 🟡 Medium |
| 375 | Longest Increasing Subsequence | 300 | DP — LIS / Subsequences | 🟡 Medium |
| 376 | Count Different Palindromic Subsequences | 730 | DP — LIS / Subsequences | 🔴 Hard |
| 377 | Longest Common Subsequence | 1143 | DP — Strings | 🟡 Medium |
| 378 | Edit Distance | 72 | DP — Strings | 🔴 Hard |
| 379 | Longest Palindromic Subsequence | 516 | DP — Strings | 🟡 Medium |
| 380 | Distinct Subsequences | 115 | DP — Strings | 🔴 Hard |
| 381 | Burst Balloons | 312 | DP — Interval | 🔴 Hard |
| 382 | Min Cost to Cut a Stick | 1547 | DP — Interval | 🔴 Hard |
| 383 | Matrix Chain Multiplication | — | DP — Interval | 🔴 Hard |
| 384 | Strange Printer | 664 | DP — Interval | 🔴 Hard |
| 385 | Minimum Cost to Merge Stones | 1000 | DP — Interval | 🔴 Hard |
| 386 | Remove Boxes | 546 | DP — Interval | 🔴 Hard |
| 387 | Knight Probability in Chessboard | 688 | DP — Probability | 🟡 Medium |
| 388 | Dice Roll Simulation | 1223 | DP — Probability | 🟡 Medium |
| 389 | Soup Servings | 808 | DP — Probability | 🟡 Medium |
| 390 | New 21 Game | 837 | DP — Probability | 🟡 Medium |
| 391 | Number of Ways | — | DP — Climbing Stairs | 🟢 Easy |
| 392 | Decode Ways II | — | DP — Strings | 🔴 Hard |
| 393 | Longest Palindromic Substring | 5 | DP — Strings | 🟡 Medium |
| 394 | Word Break | 139 | DP — Unbounded | 🟡 Medium |
| 395 | Jump Game II | 45 | DP — Greedy | 🟡 Medium |
| 396 | House Robber II | 213 | DP — Fibonacci | 🟡 Medium |
| 397 | Maximal Square | 221 | DP — Grid | 🟡 Medium |
| 398 | Two Boxes | 1467 | DP — Probability | 🔴 Hard |