Archives

How rate limiting works: token bucket, leaky bucket, fixed window counter, and sliding window log/counter algorithms with ASCII diagrams, source code walkthrough from Nginx, Guava, and Redis, and practical trade-offs.

Solutions for LeetCode 2452, medium, tags: array, string, trie.

How DNS resolution works: the recursive and iterative query process, DNS record types, caching layers, TTL mechanics, and how the global DNS hierarchy routes billions of lookups every day.

Solutions for LeetCode 907, medium, tags: array, dynamic programming, stack, monotonic stack.

Solutions for LeetCode 300, medium, tags: array, binary search, dynamic programming.

Solutions for LeetCode 15, medium, tags: array, two pointers, sorting, hash table.

Solutions for LeetCode 33, medium, tags: array, binary search.

How database query optimizers work: parsing SQL into trees, generating candidate plans, cost estimation, join ordering with dynamic programming and genetic algorithms, and a source code walkthrough of the PostgreSQL optimizer.

How the Transformer attention mechanism works: intuition behind queries/keys/values, scaled dot-product attention, multi-head attention, positional encoding, and a source code walkthrough from PyTorch and the original paper.

Solutions for LeetCode 230, medium, tags: tree, depth-first search, binary search tree, binary tree.

Solutions for LeetCode 347, medium, tags: array, hash table, divide and conquer, sorting, heap, bucket sort, counting, quickselect.

How TLS (Transport Layer Security) works: the handshake protocol, certificate verification, key exchange with Diffie-Hellman, symmetric encryption, TLS 1.2 vs 1.3, and a source code walkthrough from Go's crypto/tls package.

How Apache Kafka works internally: the distributed commit log, partitions, replication with ISR, producer batching, consumer groups, zero-copy transfer, and source code walkthrough from the apache/kafka repository.

Solutions for LeetCode 49, medium, tags: array, hash table, string, sorting.

Solutions for LeetCode 155, medium, tags: stack, design.

How gRPC works under the hood: Protocol Buffers serialization, HTTP/2 framing, the four RPC patterns (unary, server streaming, client streaming, bidirectional), channel and transport architecture, interceptors, and a source code walkthrough from the grpc/grpc-go repository.

Solutions for LeetCode 238, medium, tags: array, prefix sum.

Solutions for LeetCode 560, medium, tags: array, hash table, prefix sum.

How garbage collection works in practice: reference counting vs. tracing, mark-and-sweep fundamentals, tri-color marking, Go's concurrent collector, write barriers, GC pacing, and source code walkthrough from the Go runtime.

Solutions for LeetCode 76, hard, tags: hash table, string, sliding window.

Solutions for LeetCode 416, medium, tags: array, dynamic programming, bit manipulation.

How Bloom filters work: the probabilistic data structure behind fast membership testing in databases, with a source code walkthrough of LevelDB and RocksDB implementations.

Solutions for LeetCode 42, hard, tags: array, two pointers, dynamic programming, stack, monotonic stack.

How skip lists work: the probabilistic data structure behind Redis sorted sets, LevelDB memtables, and Java's ConcurrentSkipListMap. Covers the layered linked-list architecture, search/insert/delete algorithms, probabilistic balancing, and real-world source code walkthrough.

Solutions for LeetCode 152, medium, tags: array, dynamic programming.

How MVCC works in databases: the concurrency problem it solves, snapshot isolation, PostgreSQL's tuple versioning with xmin/xmax, MySQL InnoDB's undo log and ReadView, garbage collection, and source code walkthrough.

How Kubernetes schedules pods: the default kube-scheduler's filter-score pipeline, the scheduling framework's extension points, custom schedulers (TiDB scheduler as case study), and how Karpenter complements scheduling by provisioning nodes.

How to set up a local Kubernetes cluster with k3d for development: cluster creation, port mapping with NodePort, Mac vs Linux access patterns, kubectl port-forward vs NodePort, and why ctr digest errors are harmless.

Solutions for LeetCode 1848, easy, tags: array.

Solutions for LeetCode 394, medium, tags: string, stack, recursion.

How B+ trees work: node structure, search, insertion with splits, deletion with merges, disk I/O optimization, and why virtually every relational database uses them for indexing.

How Write-Ahead Logging (WAL) works: the core protocol behind database durability and crash recovery. Covers the WAL principle, record structure, buffer management, checkpoints, crash recovery, and a source code walkthrough from PostgreSQL.

Solutions for LeetCode 56, medium, tags: array, sorting.

Solutions for LeetCode 215, medium, tags: array, divide and conquer, sorting, heap, quick select.

How Log-Structured Merge Trees (LSM Trees) work: the write-optimized data structure behind RocksDB, LevelDB, Cassandra, and TiKV. Covers memtable, WAL, SSTables, compaction strategies, bloom filters, and a source code walkthrough from the facebook/rocksdb repository.

How consistent hashing works: the problem with naive hashing, the hash ring, virtual nodes, real-world usage in DynamoDB and Memcached, and a source code walkthrough of Go's jump consistent hash and ketama implementations.

Solutions for LeetCode 200, medium, tags: array, depth-first search, breadth-first search, union find, matrix.

Solutions for LeetCode 739, medium, tags: array, stack, monotonic stack.

How the Raft consensus algorithm works: leader election, log replication, safety guarantees, and a source code walkthrough of the etcd/raft implementation in Go.

artificial intelligence machine learning, understanding precision, recall, accuracy, confusion matrix, and the tradeoffs between them in classification problems

Solutions for LeetCode 3, medium, tags: hash table, string, sliding window.

Solutions for LeetCode 378 and LintCode 1272, medium, tags: array, binary search, heap, matrix.

Solutions for LeetCode 3653, medium, tags: array, simulation.

system design basics - Envoy proxy, north-south vs east-west traffic, its operating modes, how it competes with Nginx, and its relationship with Istio.

system design basics - forward proxy vs reverse proxy, differences, use cases, and examples

Solutions for LeetCode 874, medium, tags: array, hash table, simulation.

Solutions for LeetCode 631, hard, tags: design, graph, depth-first search, topological sort.

Solutions for LeetCode 721, medium, tags: array, hash table, string, depth-first search, breadth-first search, union find, sorting.

How TiDB's Timestamp Oracle (TSO) works: architecture, 64-bit timestamp layout, allocation algorithm, etcd persistence, client batching, and source code walkthrough from the tikv/pd repository.

Solutions for LeetCode 638, medium, tags: array, dynamic programming, backtracking, bitmask, memoization.

Solutions for LeetCode 1298, hard, tags: array, breadth-first search, graph.

Solutions for LeetCode 1235, hard, tags: array, binary search, dynamic programming, sorting.

Solutions for LeetCode 3212, medium, tags: array, matrix, prefix sum.

Solutions for LeetCode 1727, medium, tags: array, matrix, sorting.

Solutions for LeetCode 1980, medium, tags: array, hash table, string.

Shamma Elite Warriors Sandals Review

Xero DIY Sandal Review

system design basics - load balancing

Solutions for LeetCode 23 and LintCode 104, hard, tags: heap, divide and conquer, linked list, merge sort.

system design basics, all about caching (cache)

Solutions for LeetCode 21 and LintCode 165, easy, tags: heap, divide and conquer, linked list, merge sort, companies: microsoft

Solutions for LeetCode 658 LintCode 460, medium, tags: array, binary-search, sliding-window, sorting, heap; companies: google.

Solutions for LeetCode 2539 LintCode 3855, hard, tags: enumerate, string, hash table, math, combinatorics, counting.

How do websockets work comparing to http? System Design Basics, websockets

Solutions for LeetCode 2450 LintCode 3841, medium, tags: math, string.

Solutions for LeetCode 206 LintCode 35, easy, tags: linked list, recursion; companies: bytedance.

Solutions for LeetCode 1166 LintCode 3677, medium, tags: hash table, trie, string, design.

how should we interview other job candidates to find the teammates we like? tips and suggestions on how to interview teammate or junior engineers.

Solutions for LeetCode 2017, medium, tags: array, prefix sum, dynamic programming, matrix.

Solutions for LeetCode 542, LeetCode 1765, and LintCode 974, hard, tags: array, queue, sliding window, heap, monotonic queue.

Solutions for LeetCode 532 LintCode 1187, medium, tags: array, hash table, counting, two-pointers, binary-search; companies: nvidia, amazon.

Solutions for meeting rooms derivative question, hard, tags: heap, line sweep, ordered map; companies: salesforce.

Solutions for LeetCode 1400, medium, tags: hash table, string, greedy, counting.

Solutions for LeetCode 916 LintCode 1726, medium, tags: array, hash table, string.

event loop system design pattern/construct event loop (message dispatcher), reactor/actor pattern, non-blocking mechanism for concurrent applications

Solutions for LeetCode 1930, medium, tags: hash table, string, bit manipulation, prefix sum.

Solutions for , easy, tags: array, sliding window; companies: salesforce.

Solutions for LeetCode 2559, medium, tags: array, string, prefix-sum.

Solutions for LeetCode 1422, easy, tags: string, prefix sum.

Solutions for HackerRank Programmer Strings, hard, tags: string, hash table.

Solutions for LeetCode 2466 LintCode 3854, medium, tags: array, dynamic programming.

tips for using java

Solutions for LeetCode 875 LintCode 1492, medium, tags: array, binary search; companies: facebook, salesforce.

Solutions for LeetCode 423 LintCode 1247, medium, tags: hash table, simulation, math, string.

Solutions for LeetCode 239, hard, tags: array, queue, sliding window, heap, monotonic queue.

Solutions for LintCode 2503, tags: lock, re-entrant lock.

Solutions for LeetCode 239, hard, tags: array, queue, sliding window, heap, monotonic queue.

Solutions for LeetCode 339 LintCode 551, medium, tags: dfs, bfs; companies: salesforce.

Analyze Recursive Algorithm Time Complexity for LeetCode Questions with Substitution, Recursion Tree and Master Theorem

generative AI (artificial intelligence) machine learning with large language models

Solutions for LeetCode 994 LintCode 3726, medium, tags: graph, bfs, array; companies: tiktok.

Solutions for LeetCode 520 LintCode 1202, hard, tags: array, heap, greedy, sorting, binary search, dynamic programming, quick select.

Explanation for rust data structure for tree node and linked list node. What is Rc and RefCell? Why Option<Rc<RefCell>>> three wrappers? How to avoid circular reference?

Solutions for LeetCode 2558, easy, tags: array, heap, simulation.

Solutions for LeetCode 713 and LintCode 1075, medium, tags: sliding window, two pointers, prefix sum; companies: salesforce, yatra.

Solutions for LeetCode 1650 LintCode 474, medium, tags: binary tree, hash table, two pointers; companies: microsoft.

Solutions for LeetCode 408 LintCode 637, easy, tags: two pointers, string, companies: facebook, google.

tips for using AWS

Solutions for LintCode 26, hard, tags: dynamic programming.

tips for matplotlib python draw arcs, robot walks, project euler 208

Solutions for LeetCode 540 LintCode 1183, medium, tags: array, binary search.

tips for linux commands and tips

Solutions for LeetCode 1 LintCode 56, easy, tags: array, hash table.

Solutions for project euler 208 and hackerrank question robot walks, hard, tags: math, simulation.

Solutions for LeetCode 53 and LintCode 41, medium, tags: array, divide and conquer, dynamic programming, prefix sum, companies: ltk.

tips for installing sortedcontainers in a python shell

Solutions for LeetCode 1041 LintCode 1345 GFG HackerRank, medium, tags: math, string, simulation, companies: linkedin, salesforce.

Solutions for LintCode 3127, easy, tags: math, bit.

Solutions for LeetCode 1346, easy, tags: array, hash table, two pointers, binary search, sorting.

Solutions for LeetCode 91, medium, tags: string, dynamic programming, companies: goldman sachs, vmware, salesforce.

cheatsheet for math knowledge needed for leetcode algorithm questions, geometric series sum

Solutions for hackerrank bitwise xor operations, medium, tags: bit, companies: salesforce.

Fun bitwise tricks such as count set bits, negate, ilog2, xor swap, .etc.

Solutions for LeetCode 3167 HackerRank Better Compression, tags: string, hash table, companies: salesforce.

Solutions for LeetCode 239, LintCode 678, medium, tags: two pointers, string, kmp, rabin-karp, rolling hash.

Solutions for LeetCode 146 LintCode 134, medium, tags: hash, linked list, design, doubly linked list, companies: amazon, openai.

Solutions for LeetCode 487, LintCode 833, medium, tags: array, dynamic programming, sliding window, two pointers, companies: google.

Solutions for LeetCode 1 similar, medium, tags: array, hash table, companies: salesforce.

Solutions for LeetCode 811 and LintCode 1006, medium, tags: array, hash, string, counting, companies: salesforce.

Solutions for LeetCode 1804 LintCode 3729, medium, tags: design, trie, hash, string.

Solutions for LeetCode 38, LintCode 420, medium, tags: math, string, simulation, companies: facebook, pinterest.

Solutions for LeetCode 38, LintCode 420, medium, tags: math, string, simulation, companies: facebook, pinterest.

three main ways to embed an SVG image or picture as a file or using html code on a website

tips for using vim

Solutions for LeetCode 465 LintCode 707, hard, tags: bit, array, dynamic programming, backtracking, bitmask.

Solutions for Elevator Shortest Path, medium, tags: array, binary search.

Solutions for LeetCode 2257, medium, tags: array, graph, simulation.

tips for using google voice, mark all as read

Solutions for LeetCode 2461, medium, tags: array, sliding window, hash.

Solutions for LeetCode 1652, easy, tags: array, sliding window.

Solutions for LeetCode 1055 LintCode 3652, hard, tags: greedy, two pointers, string.

Solutions for LintCode 2894, medium, tags: map, sort. Related to LeetCode 884 and 451.

Solutions for LeetCode 862, LintCode 1507, hard, tags: array, queue, sliding window, heap, monotonic queue, binary search, prefix sum.

Solutions for LeetCode 3254, medium, tags: array, sliding window.

Solutions for LeetCode 125, LintCode 415, easy, tags: two pointers, string. Companies: LinkedIn, Facebook, Uber, Zenefits, Microsoft.

Solutions for LeetCode 1930, medium, tags: hash, string, bit, prefix sum.

Solutions for LeetCode 2064, medium, tags: array, binary search, heap.

Solutions for LeetCode 2563, medium, tags: array, two pointers, binary search, sorting.

solutions for LeetCode 3043, hard, tags: trie, string, array, hash.

solution for lintcode 179 update bits, tags: bit

add discord and disqus to this site

solutions for LeetCode 314 LintCode 651 Binary Tree Vertical Order Traversal, tags: hash, bfs, tree, companies: facebook google

solutions for LeetCode 1192, LintCode 1271, hard, tags: dfs, graph, bi-connected component. Companies: Amazon.

solutions for LeetCode 239, LintCode 362, hard, tags: array, queue, sliding window, heap, monotonic queue. Companies: Amazon, Zenefits, Microsoft, Google.

Solutions for LeetCode 1574, medium, tags: array, binary-search, two-pointers.

Solution for leetcode 3133 Minimum Array End, tags: bit

solution for leetcode 3097 Shortest Subarray With OR at Least K II, tags: bit, sliding-window, array

solution for LeetCode 20 LintCode 423 valid parentheses, tags: stack, string; companies: goldman sachs, twitter, airbnb, amazon, facebook, microsoft, bloomberg, uber, google.

tips for using databases including mongodb, microsoft sql server, mysql

tips for software development in Windows Operating System

tips and cheatsheet for python data/AI projects using conda, docker, and jupyter notebook

tips for using mac