| 1 | Binary Search: Find a Target in a Sorted Array in O(log n) | Easy | coding | |
| 2 | Contains Duplicate: Detect Whether Any Value Appears Twice | Easy | coding | |
| 3 | Invert Binary Tree: Recursive and Iterative Mirror Solutions | Easy | coding | |
| 4 | Linked List Cycle: Floyd's Fast and Slow Pointers | Easy | coding | |
| 5 | Majority Element: Find the Value That Fills More Than Half the Array | Easy | coding | |
| 6 | Maximum Depth of Binary Tree: Recursive DFS, Iterative DFS and BFS | Easy | coding | |
| 7 | Merge Two Sorted Lists: Dummy Head Iteration and Recursion | Easy | coding | |
| 8 | Move Zeroes: Shift Zeros to the End While Keeping Order | Easy | coding | |
| 9 | Reverse Linked List: Iterative and Recursive Solutions | Easy | coding | |
| 10 | Two Sum: Find Two Indices That Add Up to a Target | Easy | coding | |
| 11 | Valid Anagram: Check Whether Two Strings Use the Same Letters | Easy | coding | |
| 12 | Valid Palindrome: Check a Phrase While Ignoring Case and Punctuation | Easy | coding | |
| 13 | 3Sum: Find All Unique Triplets That Sum to Zero | Medium | coding | |
| 14 | Add Two Numbers: Digit-by-Digit Addition on Linked Lists | Medium | coding | |
| 15 | Clone Graph: Deep-Copy a Connected Graph with a Hash Map and BFS or DFS | Medium | coding | |
| 16 | Combination Sum II: Use Each Value Once and Avoid Duplicate Answers | Medium | coding | |
| 17 | Combination Sum: Reach a Target with Reusable Values via Backtracking | Medium | coding | |
| 18 | Container With Most Water: Maximise Area Between Two Lines | Medium | coding | |
| 19 | Copy List with Random Pointer: Hash Map and Interleaving Solutions | Medium | coding | |
| 20 | Course Schedule II: Return a Valid Course Order with Topological Sort | Medium | coding | |
| 21 | Course Schedule: Detect a Cycle in a Prerequisite Graph with Kahn's Algorithm | Medium | coding | |
| 22 | Encode and Decode Strings: Serialise a List of Strings Safely | Medium | coding | |
| 23 | Find First and Last Position of a Value: Lower and Upper Bound Binary Search | Medium | coding | |
| 24 | Find Minimum in Rotated Sorted Array: Binary Search Against the Right End | Medium | coding | |
| 25 | Find the Duplicate Number: Cycle Detection on an Array | Medium | coding | |
| 26 | Graph Valid Tree: Check Edge Count, Connectivity and Cycles with Union-Find | Medium | coding | |
| 27 | Group Anagrams: Bucket Words That Share the Same Letters | Medium | coding | |
| 28 | Insert Interval: Add a Range to a Sorted List and Merge Overlaps | Medium | coding | |
| 29 | Koko Eating Bananas: Binary Search on the Answer | Medium | coding | |
| 30 | Letter Combinations of a Phone Number: Cartesian Product by Backtracking | Medium | coding | |
| 31 | Longest Consecutive Sequence: Longest Run of Consecutive Integers in O(n) | Medium | coding | |
| 32 | LRU Cache: Hash Map Plus Doubly Linked List for O(1) Operations | Medium | coding, architecture | |
| 33 | Max Area of Island: Largest Connected Land Region with Flood Fill | Medium | coding | |
| 34 | Maximum Subarray: Largest Sum of a Contiguous Slice with Kadane's Algorithm | Medium | coding | |
| 35 | Merge Intervals: Combine Every Overlapping Range | Medium | coding | |
| 36 | Non-overlapping Intervals: Fewest Removals to Eliminate Overlaps | Medium | coding | |
| 37 | Number of Connected Components in an Undirected Graph with Union-Find | Medium | coding | |
| 38 | Number of Islands: Count Connected Land Cells with BFS, DFS or Union-Find | Medium | coding | |
| 39 | Pacific Atlantic Water Flow: Reverse Multi-Source BFS from Both Oceans | Medium | coding | |
| 40 | Palindrome Partitioning: Split a String into Palindromes by Backtracking | Medium | coding | |
| 41 | Permutations: Every Ordering of Distinct Values with Backtracking | Medium | coding | |
| 42 | Product of Array Except Self: Prefix and Suffix Products Without Division | Medium | coding | |
| 43 | Redundant Connection: Find the Edge That Closes a Cycle with Union-Find | Medium | coding | |
| 44 | Remove Nth Node From End of List: One Pass with a Gap of n | Medium | coding | |
| 45 | Reorder List: Find the Middle, Reverse, Then Interleave | Medium | coding | |
| 46 | Rotate Image: Turn a Square Matrix 90 Degrees Clockwise in Place | Medium | coding | |
| 47 | Rotting Oranges: Minutes to Spread via Level-by-Level Multi-Source BFS | Medium | coding | |
| 48 | Search a 2D Matrix: Binary Search over a Flattened Sorted Grid | Medium | coding | |
| 49 | Search in Rotated Sorted Array: One-Pass Binary Search | Medium | coding | |
| 50 | Set Matrix Zeroes: Zero Out Rows and Columns in Place | Medium | coding | |
| 51 | Sort Colors: One-Pass Three-Way Partition of 0s, 1s and 2s | Medium | coding | |
| 52 | Spiral Matrix: Read a Grid in Clockwise Spiral Order | Medium | coding | |
| 53 | Subarray Sum Equals K: Count Contiguous Slices With a Given Sum | Medium | coding | |
| 54 | Subsets II: Power Set Without Duplicates When Values Repeat | Medium | coding | |
| 55 | Subsets: Generate the Power Set with Include/Exclude Backtracking | Medium | coding | |
| 56 | Surrounded Regions: Capture Enclosed Cells by Flood-Filling from the Border | Medium | coding | |
| 57 | Time Based Key-Value Store: Versioned Lookups with Binary Search | Medium | coding, architecture | |
| 58 | Top K Frequent Elements: Return the k Most Common Values | Medium | coding | |
| 59 | Two Sum II: Find a Pair With a Target Sum in a Sorted Array | Medium | coding | |
| 60 | Valid Sudoku: Check Rows, Columns and Boxes for Repeated Digits | Medium | coding | |
| 61 | Word Search: Trace a Word Through a Letter Grid with DFS Backtracking | Medium | coding | |
| 62 | Median of Two Sorted Arrays: Partition Binary Search in O(log min(m, n)) | Hard | coding | |
| 63 | Merge k Sorted Lists: Min-Heap and Divide-and-Conquer Solutions | Hard | coding | |
| 64 | N-Queens: Place Non-Attacking Queens Row by Row with Backtracking | Hard | coding | |
| 65 | Reverse Nodes in k-Group: In-Place Group Reversal on a Linked List | Hard | coding | |
| 66 | Trapping Rain Water: Total Water Held Between Elevation Bars | Hard | coding | |
| 67 | Word Search II: Find Many Words in a Grid with a Trie and Backtracking | Hard | coding | |