Module 1: Foundations
Arrays
Traversal, in-place mutation, prefix sums and the running-aggregate patterns (Kadane's algorithm) that every later topic builds on.
36 Problems16 PatternsBeginner → Advanced
What is an Array?
Arrays are the first data structure most interview problems build on: contiguous memory, O(1) index access, and a set of traversal and two-pointer patterns that reappear across every other topic in this course.
Key ideas
- Reason about time and space complexity of common array operations
- Recognise when a single-pass running-aggregate solves a problem that looks like it needs nested loops
- Apply prefix sums to answer range-sum questions in O(1) after O(n) preprocessing
Recommended Learning Order
- 01Basic Traversal2 problems
- 02In-place Manipulation1 problem
- 03Prefix Sum3 problems
- 04Sliding Window3 problems
- 05Hashing4 problems
- 06Index Mapping1 problem
- 07Running Minimum1 problem
- 08Greedy Array Patterns3 problems
- 09Kadane's Algorithm3 problems
- 10Boyer-Moore Voting2 problems
- 11Two Pointers8 problems
- 12Dutch National Flag2 problems
- 13Prefix/Suffix Products1 problem
- 14Index Marking1 problem
- 15Difference Array1 problem
Learning tracks
- Essential
- 13problems
- Must Do problems only
- Interview Ready
- 28problems
- Must Do + Recommended
- Complete Mastery
- 36problems
- Every curated problem
Problems
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Showing 36 of 36 problems
Best Time to Buy and Sell Stock II
MediumRecommendedGreedy Array Patterns
Best Time to Buy and Sell Stock II
MediumRecommendedGreedy Array Patterns
| Status | Problem | Pattern | Difficulty | Priority | Article | Video | Solve |
|---|---|---|---|---|---|---|---|
| Reverse an Array | Basic Traversal | Easy | Optional | Read | Coming Soon | Solve | |
| Second Largest Element in an Array | Basic Traversal | Easy | Optional | Read | Coming Soon | Solve | |
| Plus One | In-place Manipulation | Easy | Optional | Read | Coming Soon | Solve | |
| Running Sum of 1d Array | Prefix Sum | Easy | Optional | Read | Coming Soon | Solve | |
| Maximum Consecutive Ones | Sliding Window | Easy | Optional | Read | Coming Soon | Solve | |
| Two Sum | Hashing | Easy | Must Do | Read | Coming Soon | Solve | |
| Contains Duplicate | Hashing | Easy | Recommended | Read | Coming Soon | Solve | |
| Missing Number | Index MappingHashing | Easy | Recommended | Read | Coming Soon | Solve | |
| Best Time to Buy and Sell Stock | Running Minimum | Easy | Must Do | Read | Coming Soon | Solve | |
| Best Time to Buy and Sell Stock II | Greedy Array Patterns | Medium | Recommended | Read | Coming Soon | Solve | |
| Maximum Subarray | Kadane's Algorithm | Medium | Must Do | Read | Coming Soon | Solve | |
| Maximum Product Subarray | Kadane's Algorithm | Medium | Must Do | Read | Coming Soon | Solve | |
| Maximum Sum Circular Subarray | Kadane's Algorithm | Medium | Recommended | Read | Coming Soon | Solve | |
| Majority Element | Boyer-Moore Voting | Easy | Must Do | Read | Coming Soon | Solve | |
| Majority Element II | Boyer-Moore Voting | Medium | Optional | Read | Coming Soon | Solve | |
| Jump Game | Greedy Array Patterns | Medium | Must Do | Read | Coming Soon | Solve | |
| Jump Game II | Greedy Array Patterns | Medium | Recommended | Read | Coming Soon | Solve | |
| Move Zeroes | Two Pointers | Easy | Must Do | Read | Coming Soon | Solve | |
| Remove Duplicates from Sorted Array | Two Pointers | Easy | Recommended | Read | Coming Soon | Solve | |
| Segregate 0s and 1s | Dutch National FlagTwo Pointers | Easy | Optional | Read | Coming Soon | Solve | |
| Sort Colors | Dutch National FlagTwo Pointers | Medium | Must Do | Read | Coming Soon | Solve | |
| Squares of a Sorted Array | Two Pointers | Easy | Recommended | Read | Coming Soon | Solve | |
| Pair with Given Sum in Sorted Array | Two Pointers | Medium | Recommended | Read | Coming Soon | Solve | |
| Container With Most Water | Two Pointers | Medium | Must Do | Read | Coming Soon | Solve | |
| Sort Array By Parity | Two PointersPartitioning | Easy | Optional | Read | Coming Soon | Solve | |
| 3Sum | Two PointersHashing | Medium | Must Do | Read | Coming Soon | Solve | |
| Trapping Rain Water | Two PointersPrefix Sum | Hard | Must Do | Read | Coming Soon | Solve | |
| Range Sum Query — Immutable | Prefix Sum | Easy | Recommended | Read | Coming Soon | Solve | |
| Find Pivot Index | Prefix Sum | Easy | Recommended | Read | Coming Soon | Solve | |
| Product of Array Except Self | Prefix/Suffix Products | Medium | Must Do | Read | Coming Soon | Solve | |
| Subarray Sum Equals K | HashingPrefix Sum | Medium | Must Do | Read | Coming Soon | Solve | |
| Longest Subarray With Sum K | HashingPrefix Sum | Medium | Recommended | Read | Coming Soon | Solve | |
| Find All Duplicates in an Array | Index MarkingHashing | Medium | Recommended | Read | Coming Soon | Solve | |
| Range Addition | Difference Array | Medium | Recommended | Read | Coming Soon | Solve | |
| Maximum Sum Subarray of Size K | Sliding Window | Easy | Recommended | Read | Coming Soon | Solve | |
| Smallest Subarray with Sum ≥ Target | Sliding Window | Medium | Recommended | Read | Coming Soon | Solve |