7 min read Core Entities Document: (doc_id, title, owner_id, workspace_id, current_version_id, status=ACTIVE|ARCHIVED|DELETED, created_at, updated_at). DocumentVersion: (version_id, doc_id, version_number, content_url, content_hash, size_bytes, created_by, created_at, […] Read article
6 min read What Is an Online Judge? An online judge (LeetCode, HackerRank, Codeforces) accepts code submissions in multiple languages, executes them against Read article
7 min read Bellman-Ford Algorithm Finds shortest paths from a source to all nodes, handling negative edge weights. Algorithm: initialize dist[source]=0, dist[all others]=inf. Read article
6 min read Requirements and Scale Search autocomplete suggests query completions as the user types. Design constraints: latency must be under 100ms (users Read article
6 min read Core Entities Policy: (policy_id, policyholder_id, policy_type=AUTO|HOME|HEALTH|LIFE, coverage_amount_cents, premium_cents, deductible_cents, start_date, end_date, status=ACTIVE|EXPIRED|CANCELLED). Claim: (claim_id, policy_id, claimant_id, incident_date, reported_date, claim_type, description, Read article
5 min read GCD and LCM Greatest Common Divisor (GCD): the largest number that divides both a and b. Euclidean algorithm: gcd(a, b) Read article
6 min read Core Entities Property: (property_id, listing_type=SALE|RENT, status=ACTIVE|PENDING|SOLD|WITHDRAWN, address, geo_point, price_cents, bedrooms, bathrooms, sqft, year_built, property_type=HOUSE|CONDO|APARTMENT|LAND, description, agent_id, created_at). PropertyImage: (image_id, property_id, Read article
6 min read The Feed Problem A social network feed shows a user the recent posts from people they follow, ranked by relevance Read article
6 min read Core Entities Coupon: (coupon_id, code, discount_type=PERCENTAGE|FIXED_AMOUNT|FREE_SHIPPING|BUY_X_GET_Y, discount_value, min_order_amount_cents, max_discount_cents, start_date, end_date, is_active, usage_limit_global, usage_limit_per_user, applicable_to=ALL|CATEGORY|PRODUCT, applicable_ids[]). CouponUsage: (usage_id, coupon_id, user_id, Read article
7 min read Segment Tree A segment tree answers range queries (range sum, range minimum) in O(log n) and supports point or range Read article
6 min read Core Entities Board: (board_id, workspace_id, name, visibility=PUBLIC|PRIVATE, owner_id, created_at). A board represents a project. Column: (column_id, board_id, name, position, wip_limit). Read article
6 min read Why Sharding? A single database server has limits: storage capacity (~tens of terabytes), write throughput (~tens of thousands of writes/second), Read article
4 min read Core Entities Wallet: (wallet_id, user_id, currency, balance_cents, status=ACTIVE|FROZEN|CLOSED, created_at). One user may have multiple wallets (different currencies). LedgerEntry: (entry_id, wallet_id, Read article
6 min read The Consensus Problem In a distributed system, multiple nodes must agree on a single value (which node is the leader, Read article
6 min read Core Entities LeaveType: (leave_type_id, name, accrual_rate_days_per_month, max_balance_days, carry_over_max_days, is_paid, requires_documentation). Examples: Annual Leave (1.67 days/month, max 30 days), Sick Leave Read article
