Two Sum
Start with the complement lookup pattern, then move into sorted-pair and sliding-window variants.
Easy arrayhash mapcomplement lookup
LeetCode Solutions
Curated LeetCode write-ups with original summaries, pattern recognition, and clean C++ implementations aimed at interview preparation. This branch sits between the DSA notebook and the harder contest archives: the emphasis is clarity, reusable patterns, and recruiter-friendly code. Official LeetCode problems are linked on every page instead of being mirrored here.
8 published solutions
8 active categories
1 easy / 7 medium / 0 hard difficulty mix
May 21, 2026 most recently updated page
Start here
Begin with the baseline interview patterns
The first batch is intentionally small. It covers the common array, pointer, stack, traversal, and DP patterns that recur in interviews.
Categories
Pattern-first archive categories
Each category groups problems by the main interview pattern, not by difficulty alone. Only completed write-ups appear as public category pages.
Arrays 1 solved
01 Hash-map lookups, prefix-style scans, and the baseline decisions that show up in almost every interview loop.
- Focus: one-pass scans and complement lookups
- Difficulties: 1 easy / 0 medium / 0 hard
- Two Sum
Two Pointers 1 solved
02 Sorted-array pairing, duplicate control, and shrinking a search space from both ends.
- Focus: sorted scans and duplicate handling
- Difficulties: 0 easy / 1 medium / 0 hard
- 3Sum
Sliding Window 1 solved
03 Grow and shrink a window while maintaining an invariant instead of restarting every substring check.
- Focus: window invariants and frequency tracking
- Difficulties: 0 easy / 1 medium / 0 hard
- Longest Substring Without Repeating Characters
Binary Search 1 solved
04 Classic sorted-array search plus binary search on a monotone feasibility answer.
- Focus: monotone predicates and answer search
- Difficulties: 0 easy / 1 medium / 0 hard
- Koko Eating Bananas
Stack 1 solved
05 Monotonic structures and deferred answers for next-greater and range-style problems.
- Focus: monotonic stack reasoning
- Difficulties: 0 easy / 1 medium / 0 hard
- Daily Temperatures
Graph 1 solved
07 Connectivity, traversal, components, and graph state propagation.
- Focus: DFS, BFS, and component thinking
- Difficulties: 0 easy / 1 medium / 0 hard
- Number of Islands
Tree 1 solved
08 Recursive structure, subtree information, and ancestor-style reasoning.
- Focus: postorder recursion and tree invariants
- Difficulties: 0 easy / 1 medium / 0 hard
- Lowest Common Ancestor of a Binary Tree
Dynamic Programming 1 solved
09 State design, transition choices, and subproblem reuse without overcomplicating the implementation.
- Focus: state compression and transition design
- Difficulties: 0 easy / 1 medium / 0 hard
- Coin Change
Learning path
One practical order to study this section
This path optimizes for transfer. Each stage builds on recognition habits from the stage before it.
01 Build the scan baseline
3 stages Start with one-pass array scans, then learn when sorting turns a quadratic search into a pointer walk.
Arrays -> Two Pointers -> Sliding Window
02 Add decision patterns
2 stages Learn the two big interview accelerators: monotonic stacks for next-greater style queries and binary search on a monotone answer.
Stack -> Binary Search
03 Move into traversal
2 stages Practice recursive and graph traversal patterns after the pointer-based problems feel routine.
Tree -> Graph
04 Finish with optimization
1 stage Dynamic programming becomes much easier once the earlier recognition patterns are stable.
Dynamic Programming
Next branches
Categories wired for future batches
These categories are part of the archive structure already, but they do not appear as public pages until they have finished solutions.
Heap: priority queues and partial ordering Backtracking: choice trees and pruning Greedy: exchange arguments and interval choices Bitmask: subset enumeration and state compression Advanced: multi-pattern design questions
Recent additions
Latest LeetCode solution pages
Each page keeps the official link, the rendered explanation, and the exact C++ source on one page.
01
Two Pointers
02 3Sum
Return every distinct triplet whose values sum to zero without duplicating answers.
Sliding Window
03 Longest Substring Without Repeating Characters
Track the longest contiguous substring whose characters stay unique.
Stack
04 Daily Temperatures
For each day, compute how far away the next warmer temperature appears.
Graph
05 Number of Islands
Count how many connected land components appear in a binary grid.
Tree
06 Lowest Common Ancestor of a Binary Tree
Find the lowest node in a binary tree whose subtree contains both target nodes.
Arrays
Two Sum
Find the two indices in an unsorted array whose values add up to the target.