A collection of LeetCode Easy difficulty problems solved with step-by-step explanations, pattern categorization, and optimized source code.
| # | Problem | Pattern | Language | Time | Space |
|---|---|---|---|---|---|
| 1 | Two Sum | Hash Map | Python | O(n) | O(n) |
| 9 | Palindrome Number | Two Pointers | Python | O(n) | O(1) |
| 13 | Roman to Integer | Prefix Sum | Python | O(n) | O(n) |
| 14 | Longest Common Prefix | Prefix Sum | Python | O(n) | O(n) |
| 20 | Valid Parentheses | Stack & Queue | JavaScript | O(n) | O(n) |
| 21 | Merge Two Sorted Lists | Two Pointers | Python | O(n) | O(1) |
| 26 | Remove Duplicates from Sorted Array | Array / General | Python | O(n) | O(1) |
| 27 | Remove Element | Array / General | Python | O(n) | O(1) |
| 28 | Find the Index of the First Occurrence in a String | Stack & Queue | Python | O(n) | O(n) |
| 35 | Search Insert Position | Binary Search | Python | O(log n) | O(1) |
| 58 | Length of Last Word | Hash Map | Python | O(n) | O(n) |
| 66 | Plus One | Array / General | Python | O(n) | O(1) |
| 67 | Add Binary | Tree & Graph | Python | O(n) | O(n) |
| 69 | Sqrt(x) | Array / General | Python | O(n) | O(1) |
| 70 | Climbing Stairs | Array / General | Python | O(n) | O(1) |
| 83 | Remove Duplicates from Sorted List | Two Pointers | PHP | O(n) | O(1) |
| 88 | Merge Sorted Array | Array / General | PHP | O(n) | O(1) |
| 94 | Binary Tree Inorder Traversal | Tree & Graph | PHP | O(n) | O(n) |
| 100 | Same Tree | Tree & Graph | PHP | O(n) | O(n) |
| 101 | Symmetric Tree | Tree & Graph | PHP | O(n) | O(n) |
| 104 | Maximum Depth of Binary Tree | Binary Search | PHP | O(n) | O(1) |
| 108 | Convert Sorted Array to Binary Search Tree | Binary Search | PHP | O(n) | O(1) |
| 110 | Balanced Binary Tree | Binary Search | PHP | O(n) | O(1) |
| 111 | Minimum Depth of Binary Tree | Binary Search | PHP | O(n) | O(1) |
| 112 | Path Sum | Tree & Graph | PHP | O(n) | O(n) |
| 118 | Pascal's Triangle | Math & Logic | PHP | O(n) | O(1) |
| 119 | Pascal's Triangle II | Math & Logic | PHP | O(n) | O(1) |
| 121 | Best Time to Buy and Sell Stock | Array / General | PHP | O(n) | O(1) |
| 125 | Valid Palindrome | Two Pointers | PHP | O(n) | O(1) |
| 136 | Single Number | Array / General | PHP | O(n) | O(1) |
| 141 | Linked List Cycle | Fast & Slow Pointers | PHP | O(n) | O(1) |
| 144 | Binary Tree Preorder Traversal | Tree & Graph | PHP | O(n) | O(n) |
| 145 | Binary Tree Postorder Traversal | Tree & Graph | PHP | O(n) | O(n) |
| 160 | Intersection of Two Linked Lists | Two Pointers | PHP | O(n) | O(1) |
| 168 | Excel Sheet Column Title | Array / General | PHP | O(n) | O(1) |
| 169 | Majority Element | Array / General | PHP | O(n) | O(1) |
| 171 | Excel Sheet Column Number | Array / General | PHP | O(n) | O(1) |
| 175 | Combine Two Tables | Database / SQL | SQL | O(n) | O(n) |
| 181 | Employees Earning More Than Their Managers | Database / SQL | SQL | O(n) | O(n) |
| 182 | Duplicate Emails | Database / SQL | SQL | O(n) | O(n) |
| 183 | Customers Who Never Order | Database / SQL | SQL | O(n) | O(n) |
| 190 | Reverse Bits | Bit Manipulation | Python | O(n) | O(1) |
| 193 | Valid Phone Numbers | Array / General | Shell | O(n) | O(1) |
| 195 | Tenth Line | Array / General | Shell | O(n) | O(1) |
| 196 | Delete Duplicate Emails | Database / SQL | SQL | O(n) | O(n) |
| 197 | Rising Temperature | Database / SQL | SQL | O(n) | O(n) |
| 202 | Happy Number | Array / General | PHP | O(n) | O(1) |
| 203 | Remove Linked List Elements | Two Pointers | PHP | O(n) | O(1) |
| 205 | Isomorphic Strings | Array / General | PHP | O(n) | O(1) |
| 206 | Reverse Linked List | Two Pointers | PHP | O(n) | O(1) |
| 217 | Contains Duplicate | Array / General | PHP | O(n) | O(1) |
| 219 | Contains Duplicate II | Array / General | PHP | O(n) | O(1) |
| 225 | Implement Stack using Queues | Stack & Queue | PHP | O(n) | O(n) |
| 226 | Invert Binary Tree | Binary Search | PHP | O(n) | O(1) |
| 228 | Summary Ranges | Array / General | PHP | O(n) | O(1) |
| 231 | Power of Two | Array / General | PHP | O(n) | O(1) |
| 232 | Implement Queue using Stacks | Stack & Queue | PHP | O(n) | O(n) |
| 234 | Palindrome Linked List | Two Pointers | PHP | O(n) | O(1) |
| 242 | Valid Anagram | Hash Map | PHP | O(n) | O(n) |
| 257 | Binary Tree Paths | Binary Search | PHP | O(n) | O(1) |
| 258 | Add Digits | Math & Logic | PHP | O(n) | O(1) |
| 263 | Ugly Number | Array / General | PHP | O(n) | O(1) |
| 268 | Missing Number | Array / General | PHP | O(n) | O(1) |
| 278 | First Bad Version | Array / General | C++ | O(n) | O(1) |
| 283 | Move Zeroes | Array / General | C++ | O(n) | O(1) |
| 290 | Word Pattern | Hash Map | C++ | O(n) | O(n) |
| 292 | Nim Game | Array / General | C++ | O(n) | O(1) |
| 326 | Power of Three | Array / General | C++ | O(n) | O(1) |
| 338 | Counting Bits | Binary Search | C++ | O(n) | O(1) |
| 342 | Power of Four | Array / General | Python | O(n) | O(1) |
| 344 | Reverse String | Array / General | Python | O(n) | O(1) |
| 345 | Reverse Vowels of a String | Array / General | Python | O(n) | O(1) |
| 349 | Intersection of Two Arrays | Two Pointers | Python | O(n) | O(1) |
| 350 | Intersection of Two Arrays II | Two Pointers | Python | O(n) | O(1) |
| 367 | Valid Perfect Square | Array / General | Python | O(n) | O(1) |
| 374 | Guess Number Higher or Lower | Array / General | Python | O(n) | O(1) |
| 383 | Ransom Note | Array / General | Python | O(n) | O(1) |
| 387 | First Unique Character in a String | Array / General | Python | O(n) | O(1) |
| 389 | Find the Difference | Array / General | Python | O(n) | O(1) |
| 392 | Is Subsequence | Dynamic Programming | Python | O(n) | O(n) |
| 401 | Binary Watch | Tree & Graph | Python | O(n) | O(n) |
| 404 | Sum of Left Leaves | Tree & Graph | Python | O(n) | O(n) |
| 405 | Convert a Number to Hexadecimal | Hash Map | Python | O(n) | O(n) |
| 409 | Longest Palindrome | Two Pointers | Python | O(n) | O(1) |
| 412 | Fizz Buzz | Array / General | Python | O(n) | O(1) |
| 414 | Third Maximum Number | Array / General | Python | O(n) | O(1) |
| 415 | Add Strings | Array / General | Python | O(n) | O(1) |
| 434 | Number of Segments in a String | Array / General | Python | O(n) | O(1) |
| 441 | Arranging Coins | Array / General | Python | O(n) | O(1) |
| 448 | Find All Numbers Disappeared in an Array | Array / General | TypeScript | O(n) | O(1) |
| 455 | Assign Cookies | Array / General | Python | O(n) | O(1) |
| 459 | Repeated Substring Pattern | Array / General | Python | O(n) | O(1) |
| 461 | Hamming Distance | Bit Manipulation | Python | O(n) | O(1) |
| 463 | Island Perimeter | Array / General | Python | O(n) | O(1) |
| 476 | Number Complement | Hash Map | Python | O(n) | O(n) |
| 482 | License Key Formatting | Array / General | Python | O(n) | O(1) |
| 485 | Max Consecutive Ones | Array / General | TypeScript | O(n) | O(1) |
| 492 | Construct the Rectangle | Math & Logic | Python | O(n) | O(1) |
| 495 | Teemo Attacking | Array / General | Python | O(n) | O(1) |
| 496 | Next Greater Element I | Monotonic Stack | Python | O(n) | O(n) |
| 500 | Keyboard Row | Array / General | Python | O(n) | O(1) |
| 501 | Find Mode in Binary Search Tree | Binary Search | Python | O(n) | O(1) |
| 504 | Base 7 | Hash Map | Python | O(n) | O(n) |
| 506 | Relative Ranks | Array / General | Python | O(n) | O(1) |
| 507 | Perfect Number | Array / General | Python | O(n) | O(1) |
| 509 | Fibonacci Number | Array / General | Python | O(n) | O(1) |
| 511 | Game Play Analysis I | Array / General | Python | O(n) | O(1) |
| 520 | Detect Capital | Array / General | Python | O(n) | O(1) |
| 521 | Longest Uncommon Subsequence I | Dynamic Programming | Python | O(n) | O(n) |
| 530 | Minimum Absolute Difference in BST | Binary Search | Python | O(n) | O(1) |
| 541 | Reverse String II | Array / General | Python | O(n) | O(1) |
| 543 | Diameter of Binary Tree | Binary Search | Python | O(n) | O(1) |
| 551 | Student Attendance Record I | Monotonic Stack | Python | O(n) | O(n) |
| 557 | Reverse Words in a String III | Array / General | Python | O(n) | O(1) |
| 559 | Maximum Depth of N-ary Tree | Tree & Graph | Python | O(n) | O(n) |
| 561 | Array Partition | Array / General | Python | O(n) | O(1) |
| 563 | Binary Tree Tilt | Binary Search | Python | O(n) | O(1) |
| 566 | Reshape the Matrix | Tree & Graph | Python | O(n) | O(n) |
| 572 | Subtree of Another Tree | Tree & Graph | Python | O(n) | O(n) |
| 575 | Distribute Candies | Array / General | Python | O(n) | O(1) |
| 577 | Employee Bonus | Database / SQL | SQL | O(n) | O(n) |
| 584 | Find Customer Referee | Database / SQL | SQL | O(n) | O(n) |
| 586 | Customer Placing the Largest Number of Orders | Database / SQL | SQL | O(n) | O(n) |
| 589 | N-ary Tree Preorder Traversal | Tree & Graph | Python | O(n) | O(n) |
| 590 | N-ary Tree Postorder Traversal | Tree & Graph | Python | O(n) | O(n) |
| 594 | Longest Harmonious Subsequence | Dynamic Programming | Python | O(n) | O(n) |
| 595 | Big Countries | Database / SQL | SQL | O(n) | O(n) |
| 596 | Classes With at Least 5 Students | Database / SQL | SQL | O(n) | O(n) |
| 598 | Range Addition II | Array / General | Python | O(n) | O(1) |
| 599 | Minimum Index Sum of Two Lists | Array / General | Python | O(n) | O(1) |
| 605 | Can Place Flowers | Array / General | Python | O(n) | O(1) |
| 607 | Sales Person | Database / SQL | SQL | O(n) | O(n) |
| 610 | Triangle Judgement | Database / SQL | SQL | O(n) | O(n) |
| 617 | Merge Two Binary Trees | Tree & Graph | Python | O(n) | O(n) |
| 619 | Biggest Single Number | Database / SQL | SQL | O(n) | O(n) |
| 620 | Not Boring Movies | Database / SQL | SQL | O(n) | O(n) |
| 627 | Swap Sex of Employees | Database / SQL | SQL | O(n) | O(n) |
| 628 | Maximum Product of Three Numbers | Binary Search | Elixir | O(n) | O(1) |
| 637 | Average of Levels in Binary Tree | Binary Search | Python | O(n) | O(1) |
| 643 | Maximum Average Subarray I | Array / General | Python | O(n) | O(1) |
| 645 | Set Mismatch | Bit Manipulation | TypeScript | O(n) | O(1) |
| 657 | Robot Return to Origin | Array / General | Python | O(n) | O(1) |
| 661 | Image Smoother | Array / General | Python | O(n) | O(1) |
| 671 | Second Minimum Node In a Binary Tree | Two Pointers | Python | O(n) | O(1) |
| 674 | Longest Continuous Increasing Subsequence | Dynamic Programming | Python | O(n) | O(n) |
| 682 | Baseball Game | Bit Manipulation | Python | O(n) | O(1) |
| 693 | Binary Number with Alternating Bits | Two Pointers | Python | O(n) | O(1) |
| 696 | Count Binary Substrings | Tree & Graph | Python | O(n) | O(n) |
| 697 | Degree of an Array | Hash Map | Python | O(n) | O(n) |
| 700 | Search in a Binary Search Tree | Binary Search | Python | O(n) | O(1) |
| 703 | Kth Largest Element in a Stream | Array / General | Python | O(n) | O(1) |
| 704 | Binary Search | Binary Search | Python | O(log n) | O(1) |
| 705 | Design HashSet | Hash Map | Python | O(n) | O(n) |
| 706 | Design HashMap | Hash Map | Python | O(n) | O(n) |
| 709 | To Lower Case | Array / General | Python | O(n) | O(1) |
| 717 | 1-bit and 2-bit Characters | Bit Manipulation | Python | O(n) | O(1) |
| 724 | Find Pivot Index | Array / General | Python | O(n) | O(1) |
| 728 | Self Dividing Numbers | Array / General | Python | O(n) | O(1) |
| 733 | Flood Fill | Array / General | Python | O(n) | O(1) |
| 744 | Find Smallest Letter Greater Than Target | Prefix Sum | Python | O(n) | O(n) |
| 746 | Min Cost Climbing Stairs | Array / General | Python | O(n) | O(1) |
| 747 | Largest Number At Least Twice of Others | Array / General | Python | O(n) | O(1) |
| 748 | Shortest Completing Word | Hash Map | Python | O(n) | O(n) |
| 762 | Prime Number of Set Bits in Binary Representation | Two Pointers | Python | O(n) | O(1) |
| 766 | Toeplitz Matrix | Tree & Graph | Python | O(n) | O(n) |
| 771 | Jewels and Stones | Array / General | Python | O(n) | O(1) |
| 783 | Minimum Distance Between BST Nodes | Binary Search | Python | O(n) | O(1) |
| 796 | Rotate String | Math & Logic | C++ | O(n) | O(1) |
| 804 | Unique Morse Code Words | Array / General | Python | O(n) | O(1) |
| 806 | Number of Lines To Write String | Array / General | Python | O(n) | O(1) |
| 812 | Largest Triangle Area | Math & Logic | Python | O(n) | O(1) |
| 819 | Most Common Word | Array / General | Python | O(n) | O(1) |
| 821 | Shortest Distance to a Character | Array / General | Python | O(n) | O(1) |
| 824 | Goat Latin | Array / General | Python | O(n) | O(1) |
| 830 | Positions of Large Groups | Array / General | Python | O(n) | O(1) |
| 832 | Flipping an Image | Array / General | Python | O(n) | O(1) |
| 836 | Rectangle Overlap | Math & Logic | JavaScript | O(n) | O(1) |
| 844 | Backspace String Compare | Array / General | Python | O(n) | O(1) |
| 859 | Buddy Strings | Array / General | Python | O(n) | O(1) |
| 860 | Lemonade Change | Array / General | Python | O(n) | O(1) |
| 867 | Transpose Matrix | Tree & Graph | Python | O(n) | O(n) |
| 868 | Binary Gap | Tree & Graph | Python | O(n) | O(n) |
| 872 | Leaf-Similar Trees | Tree & Graph | Python | O(n) | O(n) |
| 876 | Middle of the Linked List | Two Pointers | Python | O(n) | O(1) |
| 883 | Projection Area of 3D Shapes | Array / General | Python | O(n) | O(1) |
| 884 | Uncommon Words from Two Sentences | Array / General | Python | O(n) | O(1) |
| 888 | Fair Candy Swap | Array / General | Python | O(n) | O(1) |
| 892 | Surface Area of 3D Shapes | Array / General | Python | O(n) | O(1) |
| 896 | Monotonic Array | Monotonic Stack | Python | O(n) | O(n) |
| 897 | Increasing Order Search Tree | Binary Search | Python | O(n) | O(1) |
| 905 | Sort Array By Parity | Hash Map | Python | O(n) | O(n) |
| 908 | Smallest Range I | Array / General | Python | O(n) | O(1) |
| 914 | X of a Kind in a Deck of Cards | Array / General | Python | O(n) | O(1) |
| 917 | Reverse Only Letters | Array / General | Python | O(n) | O(1) |
| 922 | Sort Array By Parity II | Array / General | Python | O(n) | O(1) |
| 925 | Long Pressed Name | Array / General | Python | O(n) | O(1) |
| 929 | Unique Email Addresses | Array / General | Python | O(n) | O(1) |
| 933 | Number of Recent Calls | Array / General | Python | O(n) | O(1) |
| 938 | Range Sum of BST | Binary Search | Python | O(n) | O(1) |
| 941 | Valid Mountain Array | Array / General | Python | O(n) | O(1) |
| 942 | DI String Match | Array / General | Python | O(n) | O(1) |
| 944 | Delete Columns to Make Sorted | Array / General | Python | O(n) | O(1) |
| 953 | Verifying an Alien Dictionary | Hash Map | Python | O(n) | O(n) |
| 961 | N-Repeated Element in Size 2N Array | Array / General | Python | O(n) | O(1) |
| 965 | Univalued Binary Tree | Binary Search | Python | O(n) | O(1) |
| 976 | Largest Perimeter Triangle | Math & Logic | Python | O(n) | O(1) |
| 977 | Squares of a Sorted Array | Array / General | Python | O(n) | O(1) |
| 989 | Add to Array-Form of Integer | Array / General | Python | O(n) | O(1) |
| 993 | Cousins in Binary Tree | Binary Search | Python | O(n) | O(1) |
| 997 | Find the Town Judge | Array / General | Python | O(n) | O(1) |
| 999 | Available Captures for Rook | Array / General | Python | O(n) | O(1) |
| 1002 | Find Common Characters | Array / General | Python | O(n) | O(1) |
| 1005 | Maximize Sum Of Array After K Negations | Array / General | Python | O(n) | O(1) |
| 1009 | Complement of Base 10 Integer | Hash Map | Python | O(n) | O(n) |
| 1018 | Binary Prefix Divisible By 5 | Prefix Sum | Python | O(n) | O(n) |
| 1021 | Remove Outermost Parentheses | Stack & Queue | Python | O(n) | O(n) |
| 1022 | Sum of Root To Leaf Binary Numbers | Tree & Graph | Python | O(n) | O(n) |
| 1025 | Divisor Game | Array / General | Python | O(n) | O(1) |
| 1030 | Matrix Cells in Distance Order | Tree & Graph | Python | O(n) | O(n) |
| 1037 | Valid Boomerang | Array / General | Python | O(n) | O(1) |
| 1046 | Last Stone Weight | Array / General | Python | O(n) | O(1) |
| 1047 | Remove All Adjacent Duplicates In String | Array / General | Python | O(n) | O(1) |
| 1050 | Actors and Directors Who Cooperated At Least Three Times | Database / SQL | SQL | O(n) | O(n) |
| 1051 | Height Checker | Array / General | Python | O(n) | O(1) |
| 1068 | Product Sales Analysis I | Database / SQL | SQL | O(n) | O(n) |
| 1071 | Greatest Common Divisor of Strings | Array / General | Python | O(n) | O(1) |
| 1075 | Project Employees I | Database / SQL | SQL | O(n) | O(n) |
| 1078 | Occurrences After Bigram | Array / General | Python | O(n) | O(1) |
| 1084 | Sales Analysis III | Database / SQL | SQL | O(n) | O(n) |
| 1089 | Duplicate Zeros | Array / General | Python | O(n) | O(1) |
| 1103 | Distribute Candies to People | Array / General | Python | O(n) | O(1) |
| 1108 | Defanging an IP Address | Array / General | Python | O(n) | O(1) |
| 1114 | Print in Order | Hash Map | Java | O(n) | O(n) |
| 1122 | Relative Sort Array | Hash Map | Python | O(n) | O(n) |
| 1128 | Number of Equivalent Domino Pairs | Array / General | Python | O(n) | O(1) |
| 1137 | N-th Tribonacci Number | Bit Manipulation | Python | O(n) | O(1) |
| 1141 | User Activity for the Past 30 Days I | Database / SQL | SQL | O(n) | O(n) |
| 1148 | Article Views I | Database / SQL | SQL | O(n) | O(n) |
| 1154 | Day of the Year | Array / General | Python | O(n) | O(1) |
| 1160 | Find Words That Can Be Formed by Characters | Tree & Graph | Python | O(n) | O(n) |
| 1175 | Prime Arrangements | Bit Manipulation | Python | O(n) | O(1) |
| 1179 | Reformat Department Table | Database / SQL | SQL | O(n) | O(n) |
| 1185 | Day of the Week | Array / General | Python | O(n) | O(1) |
| 1189 | Maximum Number of Balloons | Hash Map | Kotlin | O(n) | O(n) |
| 1200 | Minimum Absolute Difference | Array / General | Python | O(n) | O(1) |
| 1207 | Unique Number of Occurrences | Array / General | Python | O(n) | O(1) |
| 1211 | Queries Quality and Percentage | Database / SQL | SQL | O(n) | O(n) |
| 1217 | Minimum Cost to Move Chips to The Same Position | Array / General | Python | O(n) | O(1) |
| 1221 | Split a String in Balanced Strings | Array / General | Python | O(n) | O(1) |
| 1232 | Check If It Is a Straight Line | Array / General | Python | O(n) | O(1) |
| 1251 | Average Selling Price | Database / SQL | SQL | O(n) | O(n) |
| 1252 | Cells with Odd Values in a Matrix | Tree & Graph | Python | O(n) | O(n) |
| 1260 | Shift 2D Grid | Tree & Graph | Racket | O(n) | O(n) |
| 1266 | Minimum Time Visiting All Points | Array / General | Python | O(n) | O(1) |
| 1275 | Find Winner on a Tic Tac Toe Game | Array / General | Python | O(n) | O(1) |
| 1280 | Students and Examinations | Database / SQL | SQL | O(n) | O(n) |
| 1281 | Subtract the Product and Sum of Digits of an Integer | Math & Logic | Python | O(n) | O(1) |
| 1287 | Element Appearing More Than 25% In Sorted Array | Array / General | Python | O(n) | O(1) |
| 1290 | Convert Binary Number in a Linked List to Integer | Binary Search | Python | O(n) | O(1) |
| 1295 | Find Numbers with Even Number of Digits | Math & Logic | Python | O(n) | O(1) |
| 1299 | Replace Elements with Greatest Element on Right Side | Array / General | Python | O(n) | O(1) |
| 1309 | Decrypt String from Alphabet to Integer Mapping | Array / General | Python | O(n) | O(1) |
| 1313 | Decompress Run-Length Encoded List | Array / General | Python | O(n) | O(1) |
| 1317 | Convert Integer to the Sum of Two No-Zero Integers | Array / General | Python | O(n) | O(1) |
| 1323 | Maximum 69 Number | Array / General | Python | O(n) | O(1) |
| 1327 | List the Products Ordered in a Period | Database / SQL | SQL | O(n) | O(n) |
| 1331 | Rank Transform of an Array | Binary Search | Kotlin | O(n) | O(1) |
| 1332 | Remove Palindromic Subsequences | Dynamic Programming | Python | O(n) | O(n) |
| 1337 | The K Weakest Rows in a Matrix | Tree & Graph | Python | O(n) | O(n) |
| 1342 | Number of Steps to Reduce a Number to Zero | Array / General | Python | O(n) | O(1) |
| 1346 | Check If N and Its Double Exist | Array / General | Python | O(n) | O(1) |
| 1351 | Count Negative Numbers in a Sorted Matrix | Tree & Graph | Python | O(n) | O(n) |
| 1356 | Sort Integers by The Number of 1 Bits | Bit Manipulation | Python | O(n) | O(1) |
| 1360 | Number of Days Between Two Dates | Array / General | Python | O(n) | O(1) |
| 1365 | How Many Numbers Are Smaller Than the Current Number | Prefix Sum | TypeScript | O(n) | O(n) |
| 1370 | Increasing Decreasing String | Array / General | Python | O(n) | O(1) |
| 1374 | Generate a String With Characters That Have Odd Counts | Array / General | Python | O(n) | O(1) |
| 1378 | Replace Employee ID With The Unique Identifier | Database / SQL | SQL | O(n) | O(n) |
| 1379 | Find a Corresponding Node of a Binary Tree in a Clone of That Tree | Binary Search | Python | O(n) | O(1) |
| 1380 | Lucky Numbers in a Matrix | Tree & Graph | Python | O(n) | O(n) |
| 1385 | Find the Distance Value Between Two Arrays | Array / General | Python | O(n) | O(1) |
| 1389 | Create Target Array in the Given Order | Array / General | Python | O(n) | O(1) |
| 1394 | Find Lucky Integer in an Array | Hash Map | Python | O(n) | O(n) |
| 1399 | Count Largest Group | Array / General | Python | O(n) | O(1) |
| 1403 | Minimum Subsequence in Non-Increasing Order | Dynamic Programming | Python | O(n) | O(n) |
| 1407 | Top Travellers | Database / SQL | SQL | O(n) | O(n) |
| 1408 | String Matching in an Array | Array / General | Python | O(n) | O(1) |
| 1413 | Minimum Value to Get Positive Step by Step Sum | Array / General | Python | O(n) | O(1) |
| 1417 | Reformat The String | Array / General | Python | O(n) | O(1) |
| 1422 | Maximum Score After Splitting a String | Array / General | Python | O(n) | O(1) |
| 1431 | Kids With the Greatest Number of Candies | Array / General | Python | O(n) | O(1) |
| 1436 | Destination City | Array / General | Python | O(n) | O(1) |
| 1437 | Check If All 1's Are at Least Length K Places Away | Array / General | Python | O(n) | O(1) |
| 1446 | Consecutive Characters | Array / General | Python | O(n) | O(1) |
| 1450 | Number of Students Doing Homework at a Given Time | Array / General | Python | O(n) | O(1) |
| 1455 | Check If a Word Occurs As a Prefix of Any Word in a Sentence | Prefix Sum | Python | O(n) | O(n) |
| 1460 | Make Two Arrays Equal by Reversing Subarrays | Array / General | Python | O(n) | O(1) |
| 1464 | Maximum Product of Two Elements in an Array | Binary Search | Scala | O(n) | O(1) |
| 1470 | Shuffle the Array | Array / General | TypeScript | O(n) | O(1) |
| 1475 | Final Prices With a Special Discount in a Shop | Monotonic Stack | TypeScript | O(n) | O(n) |
| 1480 | Running Sum of 1d Array | Array / General | Python | O(n) | O(1) |
| 1484 | Group Sold Products By The Date | Database / SQL | SQL | O(n) | O(n) |
| 1486 | XOR Operation in an Array | Bit Manipulation | Python | O(n) | O(1) |
| 1491 | Average Salary Excluding the Minimum and Maximum Salary | Array / General | Python | O(n) | O(1) |
| 1496 | Path Crossing | Tree & Graph | Python | O(n) | O(n) |
| 1502 | Can Make Arithmetic Progression From Sequence | Array / General | Python | O(n) | O(1) |
| 1507 | Reformat Date | Array / General | Python | O(n) | O(1) |
| 1512 | Number of Good Pairs | Array / General | Python | O(n) | O(1) |
| 1517 | Find Users With Valid E-Mails | Database / SQL | SQL | O(n) | O(n) |
| 1518 | Water Bottles | Array / General | Python | O(n) | O(1) |
| 1523 | Count Odd Numbers in an Interval Range | Heap | Python | O(n) | O(n) |
| 1527 | Patients With a Condition | Database / SQL | SQL | O(n) | O(n) |
| 1528 | Shuffle String | Array / General | Python | O(n) | O(1) |
| 1544 | Make The String Great | Array / General | Python | O(n) | O(1) |
| 1550 | Three Consecutive Odds | Array / General | Python | O(n) | O(1) |
| 1556 | Thousand Separator | Array / General | Python | O(n) | O(1) |
| 1566 | Detect Pattern of Length M Repeated K or More Times | Hash Map | Python | O(n) | O(n) |
| 1572 | Matrix Diagonal Sum | Tree & Graph | Python | O(n) | O(n) |
| 1581 | Customer Who Visited but Did Not Make Any Transactions | Database / SQL | SQL | O(n) | O(n) |
| 1587 | Bank Account Summary II | Database / SQL | SQL | O(n) | O(n) |
| 1588 | Sum of All Odd Length Subarrays | Array / General | C++ | O(n) | O(1) |
| 1592 | Rearrange Spaces Between Words | Array / General | C++ | O(n) | O(1) |
| 1598 | Crawler Log Folder | Array / General | C++ | O(n) | O(1) |
| 1603 | Design Parking System | Array / General | C++ | O(n) | O(1) |
| 1608 | Special Array With X Elements Greater Than or Equal X | Array / General | C++ | O(n) | O(1) |
| 1614 | Maximum Nesting Depth of the Parentheses | Stack & Queue | Java | O(n) | O(n) |
| 1619 | Mean of Array After Removing Some Elements | Array / General | C++ | O(n) | O(1) |
| 1624 | Largest Substring Between Two Equal Characters | Array / General | C++ | O(n) | O(1) |
| 1629 | Slowest Key | Array / General | C++ | O(n) | O(1) |
| 1633 | Percentage of Users Attended a Contest | Database / SQL | SQL | O(n) | O(n) |
| 1636 | Sort Array by Increasing Frequency | Hash Map | C++ | O(n) | O(n) |
| 1637 | Widest Vertical Area Between Two Points Containing No Points | Array / General | C++ | O(n) | O(1) |
| 1640 | Check Array Formation Through Concatenation | Array / General | C++ | O(n) | O(1) |
| 1646 | Get Maximum in Generated Array | Array / General | C++ | O(n) | O(1) |
| 1652 | Defuse the Bomb | Array / General | C++ | O(n) | O(1) |
| 1656 | Design an Ordered Stream | Bit Manipulation | C++ | O(n) | O(1) |
| 1661 | Average Time of Process per Machine | Database / SQL | SQL | O(n) | O(n) |
| 1662 | Check If Two String Arrays are Equivalent | Array / General | C++ | O(n) | O(1) |
| 1667 | Fix Names in a Table | Database / SQL | SQL | O(n) | O(n) |
| 1668 | Maximum Repeating Substring | Array / General | C++ | O(n) | O(1) |
| 1672 | Richest Customer Wealth | Array / General | C++ | O(n) | O(1) |
| 1678 | Goal Parser Interpretation | Array / General | C++ | O(n) | O(1) |
| 1683 | Invalid Tweets | Database / SQL | SQL | O(n) | O(n) |
| 1684 | Count the Number of Consistent Strings | Array / General | C++ | O(n) | O(1) |
| 1688 | Count of Matches in Tournament | Array / General | C++ | O(n) | O(1) |
| 1693 | Daily Leads and Partners | Database / SQL | SQL | O(n) | O(n) |
| 1694 | Reformat Phone Number | Array / General | C++ | O(n) | O(1) |
| 1700 | Number of Students Unable to Eat Lunch | Stack & Queue | C++ | O(n) | O(n) |
| 1704 | Determine if String Halves Are Alike | Array / General | C++ | O(n) | O(1) |
| 1710 | Maximum Units on a Truck | Tree & Graph | C++ | O(n) | O(n) |
| 1716 | Calculate Money in Leetcode Bank | Array / General | C++ | O(n) | O(1) |
| 1720 | Decode XORed Array | Bit Manipulation | C++ | O(n) | O(1) |
| 1725 | Number Of Rectangles That Can Form The Largest Square | Math & Logic | C++ | O(n) | O(1) |
| 1729 | Find Followers Count | Database / SQL | SQL | O(n) | O(n) |
| 1731 | The Number of Employees Which Report to Each Employee | Database / SQL | SQL | O(n) | O(n) |
| 1732 | Find the Highest Altitude | Array / General | Kotlin | O(n) | O(1) |
| 1736 | Latest Time by Replacing Hidden Digits | Math & Logic | C++ | O(n) | O(1) |
| 1741 | Find Total Time Spent by Each Employee | Database / SQL | SQL | O(n) | O(n) |
| 1742 | Maximum Number of Balls in a Box | Array / General | C++ | O(n) | O(1) |
| 1748 | Sum of Unique Elements | Array / General | C++ | O(n) | O(1) |
| 1752 | Check if Array Is Sorted and Rotated | Binary Search | C++ | O(n) | O(1) |
| 1757 | Recyclable and Low Fat Products | Database / SQL | SQL | O(n) | O(n) |
| 1758 | Minimum Changes To Make Alternating Binary String | Tree & Graph | C++ | O(n) | O(n) |
| 1763 | Longest Nice Substring | Array / General | C++ | O(n) | O(1) |
| 1773 | Count Items Matching a Rule | Array / General | C++ | O(n) | O(1) |
| 1779 | Find Nearest Point That Has the Same X or Y Coordinate | Tree & Graph | C++ | O(n) | O(n) |
| 1784 | Check if Binary String Has at Most One Segment of Ones | Bit Manipulation | C++ | O(n) | O(1) |
| 1789 | Primary Department for Each Employee | Database / SQL | SQL | O(n) | O(n) |
| 1790 | Check if One String Swap Can Make Strings Equal | Array / General | C++ | O(n) | O(1) |
| 1791 | Find Center of Star Graph | Array / General | C++ | O(n) | O(1) |
| 1795 | Rearrange Products Table | Database / SQL | SQL | O(n) | O(n) |
| 1796 | Second Largest Digit in a String | Math & Logic | C++ | O(n) | O(1) |
| 1800 | Maximum Ascending Subarray Sum | Two Pointers | C++ | O(n) | O(1) |
| 1805 | Number of Different Integers in a String | Bit Manipulation | C++ | O(n) | O(1) |
| 1812 | Determine Color of a Chessboard Square | Array / General | C++ | O(n) | O(1) |
| 1816 | Truncate Sentence | Array / General | C++ | O(n) | O(1) |
| 1822 | Sign of the Product of an Array | Array / General | C++ | O(n) | O(1) |
| 1827 | Minimum Operations to Make the Array Increasing | Hash Map | C++ | O(n) | O(n) |
| 1832 | Check if the Sentence Is Pangram | Array / General | C++ | O(n) | O(1) |
| 1837 | Sum of Digits in Base K | Math & Logic | C++ | O(n) | O(1) |
| 1844 | Replace All Digits with Characters | Math & Logic | C++ | O(n) | O(1) |
| 1848 | Minimum Distance to the Target Element | Array / General | C++ | O(n) | O(1) |
| 1854 | Maximum Population Year | Tree & Graph | C++ | O(n) | O(n) |
| 1859 | Sorting the Sentence | Array / General | C++ | O(n) | O(1) |
| 1863 | Sum of All Subset XOR Totals | Bit Manipulation | C++ | O(n) | O(1) |
| 1869 | Longer Contiguous Segments of Ones than Zeros | Array / General | C++ | O(n) | O(1) |
| 1873 | Calculate Special Bonus | Database / SQL | SQL | O(n) | O(n) |
| 1876 | Substrings of Size Three with Distinct Characters | Array / General | C++ | O(n) | O(1) |
| 1880 | Check if Word Equals Summation of Two Words | Array / General | C++ | O(n) | O(1) |
| 1886 | Determine Whether Matrix Can Be Obtained By Rotation | Tree & Graph | C++ | O(n) | O(n) |
| 1890 | The Latest Login in 2020 | Database / SQL | SQL | O(n) | O(n) |
| 1893 | Check if All the Integers in a Range Are Covered | Array / General | C++ | O(n) | O(1) |
| 1897 | Redistribute Characters to Make All Strings Equal | Array / General | C++ | O(n) | O(1) |
| 1903 | Largest Odd Number in String | Array / General | C++ | O(n) | O(1) |
| 1909 | Remove One Element to Make the Array Strictly Increasing | Array / General | C++ | O(n) | O(1) |
| 1913 | Maximum Product Difference Between Two Pairs | Array / General | C++ | O(n) | O(1) |
| 1920 | Build Array from Permutation | Backtracking | C++ | O(n) | O(1) |
| 1925 | Count Square Sum Triples | Array / General | C++ | O(n) | O(1) |
| 1929 | Concatenation of Array | Array / General | TypeScript | O(n) | O(1) |
| 1935 | Maximum Number of Words You Can Type | Array / General | C++ | O(n) | O(1) |
| 1941 | Check if All Characters Have Equal Number of Occurrences | Hash Map | C++ | O(n) | O(n) |
| 1945 | Sum of Digits of String After Convert | Math & Logic | C++ | O(n) | O(1) |
| 1952 | Three Divisors | Array / General | C++ | O(n) | O(1) |
| 1957 | Delete Characters to Make Fancy String | Array / General | C++ | O(n) | O(1) |
| 1961 | Check If String Is a Prefix of Array | Prefix Sum | C++ | O(n) | O(n) |
| 1965 | Employees With Missing Information | Database / SQL | SQL | O(n) | O(n) |
| 1967 | Number of Strings That Appear as Substrings in Word | Tree & Graph | Kotlin | O(n) | O(n) |
| 1971 | Find if Path Exists in Graph | Dynamic Programming | JavaScript | O(n) | O(n) |
| 1974 | Minimum Time to Type Word Using Special Typewriter | Array / General | JavaScript | O(n) | O(1) |
| 1978 | Employees Whose Manager Left the Company | Database / SQL | SQL | O(n) | O(n) |
| 1979 | Find Greatest Common Divisor of Array | Array / General | Kotlin | O(n) | O(1) |
| 1984 | Minimum Difference Between Highest and Lowest of K Scores | Array / General | JavaScript | O(n) | O(1) |
| 1991 | Find the Middle Index in Array | Array / General | JavaScript | O(n) | O(1) |
| 1995 | Count Special Quadruplets | Array / General | JavaScript | O(n) | O(1) |
| 2000 | Reverse Prefix of Word | Prefix Sum | JavaScript | O(n) | O(n) |
| 2144 | Minimum Cost of Buying Candies With Discount | Sliding Window | Kotlin | O(n) | O(1) |
| 2356 | Number of Unique Subjects Taught by Each Teacher | Database / SQL | SQL | O(n) | O(n) |
| 2540 | Minimum Common Value | Sliding Window | C++ | O(n) | O(1) |
| 2553 | Separate the Digits in an Array | Math & Logic | C++ | O(n) | O(1) |
| 2574 | Left and Right Sum Differences | Prefix Sum | Kotlin | O(n) | O(n) |
| 2619 | Array Prototype Last | Array / General | JavaScript | O(n) | O(1) |
| 2620 | Counter | Array / General | JavaScript | O(n) | O(1) |
| 2621 | Sleep | Array / General | JavaScript | O(n) | O(1) |
| 2626 | Array Reduce Transformation | Array / General | TypeScript | O(n) | O(1) |
| 2629 | Function Composition | Array / General | TypeScript | O(n) | O(1) |
| 2634 | Filter Elements from Array | Array / General | TypeScript | O(n) | O(1) |
| 2635 | Apply Transform Over Each Element in Array | Hash Map | TypeScript | O(n) | O(n) |
| 2648 | Generate Fibonacci Sequence | Array / General | TypeScript | O(n) | O(1) |
| 2665 | Counter II | Array / General | TypeScript | O(n) | O(1) |
| 2666 | Allow One Function Call | Array / General | TypeScript | O(n) | O(1) |
| 2667 | Create Hello World Function | Tree & Graph | TypeScript | O(n) | O(n) |
| 2677 | Chunk Array | Array / General | TypeScript | O(n) | O(1) |
| 2695 | Array Wrapper | Array / General | TypeScript | O(n) | O(1) |
| 2703 | Return Length of Arguments Passed | Hash Map | TypeScript | O(n) | O(n) |
| 2704 | To Be Or Not To Be | Array / General | TypeScript | O(n) | O(1) |
| 2723 | Add Two Promises | Bit Manipulation | TypeScript | O(n) | O(1) |
| 2724 | Sort By | Array / General | TypeScript | O(n) | O(1) |
| 2725 | Interval Cancellation | Heap | TypeScript | O(n) | O(n) |
| 2726 | Calculator with Method Chaining | Hash Map | TypeScript | O(n) | O(n) |
| 2727 | Is Object Empty | Array / General | TypeScript | O(n) | O(1) |
| 2784 | Check if Array is Good | Array / General | C++ | O(n) | O(1) |
| 2877 | Create a DataFrame from List | Two Pointers | Python | O(n) | O(1) |
| 2878 | Get the Size of a DataFrame | Two Pointers | Python | O(n) | O(1) |
| 2879 | Display the First Three Rows | Array / General | Python | O(n) | O(1) |
| 2880 | Select Data | Bit Manipulation | Python | O(n) | O(1) |
| 2881 | Create a New Column | Two Pointers | Python | O(n) | O(1) |
| 2882 | Drop Duplicate Rows | Array / General | Python | O(n) | O(1) |
| 2883 | Drop Missing Data | Bit Manipulation | Python | O(n) | O(1) |
| 2884 | Modify Columns | Tree & Graph | Python | O(n) | O(n) |
| 2885 | Rename Columns | Tree & Graph | Python | O(n) | O(n) |
| 2886 | Change Data Type | Bit Manipulation | Python | O(n) | O(1) |
| 2887 | Fill Missing Data | Bit Manipulation | Python | O(n) | O(1) |
| 2888 | Reshape Data: Concatenate | Stack & Queue | Python | O(n) | O(n) |
| 2889 | Reshape Data: Pivot | Tree & Graph | Python | O(n) | O(n) |
| 2890 | Reshape Data: Melt | Bit Manipulation | Python | O(n) | O(1) |
| 2891 | Method Chaining | Hash Map | Python | O(n) | O(n) |
| 2996 | Smallest Missing Integer Greater Than Sequential Prefix Sum | Prefix Sum | Rust | O(n) | O(n) |
| 3014 | Minimum Number of Pushes to Type Word I | Hash Map | Dart | O(n) | O(n) |
| 3069 | Distribute Elements Into Two Arrays I | Hash Map | Go | O(n) | O(n) |
| 3090 | Maximum Length Substring With Two Occurrences | Array / General | Swift | O(n) | O(1) |
| 3120 | Count the Number of Special Characters I | Array / General | C++ | O(n) | O(1) |
| 3300 | Minimum Element After Replacement With Digit Sum | Math & Logic | C++ | O(n) | O(1) |
| 3345 | Smallest Divisible Digit Product I | Tree & Graph | Ruby | O(n) | O(n) |
| 3436 | Find Valid Emails | Database / SQL | SQL | O(n) | O(n) |
| 3465 | Find Products with Valid Serial Numbers | Database / SQL | SQL | O(n) | O(n) |
| 3471 | Find the Largest Almost Missing Integer | Prefix Sum | Kotlin | O(n) | O(n) |
| 3483 | Unique 3-Digit Even Numbers | Math & Logic | JavaScript | O(n) | O(1) |
| 3498 | Reverse Degree of a String | Array / General | Python | O(n) | O(1) |
| 3536 | Maximum Product of Two Digits | Math & Logic | Erlang | O(n) | O(1) |
| 3550 | Smallest Index With Digit Sum Equal to Index | Prefix Sum | JavaScript | O(n) | O(n) |
| 3570 | Find Books with No Available Copies | Array / General | Python | O(n) | O(1) |
| 3622 | Check Divisibility by Digit Sum and Product | Math & Logic | C | O(n) | O(1) |
| 3633 | Earliest Finish Time for Land and Water Rides I | Array / General | Kotlin | O(n) | O(1) |
| 3658 | GCD of Odd and Even Sums | Array / General | Kotlin | O(n) | O(1) |
| 3718 | Smallest Missing Multiple of K | Prefix Sum | C# | O(n) | O(n) |
| 3731 | Find Missing Elements | Array / General | PHP | O(n) | O(1) |
| 3754 | Concatenate Non-Zero Digits and Multiply by Sum I | Bit Manipulation | Kotlin | O(n) | O(1) |
| 3793 | Find Users with High Token Usage | Database / SQL | SQL | O(n) | O(n) |
| 3838 | Weighted Word Mapping | Hash Map | Kotlin | O(n) | O(n) |
| 3870 | Count Commas in Range | Tree & Graph | JavaScript | O(n) | O(n) |
| 3875 | Construct Uniform Parity Array I | Binary Search | C++ | O(n) | O(1) |
| 3903 | Smallest Stable Index I | Tree & Graph | JavaScript | O(n) | O(n) |