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Cryptocurrency Exchange — Simple#

Problem statement (interviewer prompt)

Design a Coinbase-style cryptocurrency exchange: spot trading with order book + matching, deposits + withdrawals across multiple blockchains, custody (hot / warm / cold wallets), KYC/AML, market-data feeds to clients, and rock-solid ledger integrity.

flowchart LR
  U([User])
  ME[Matching Engine]
  WAL[Hot Wallet]
  CW[Cold Wallet]
  CHN[Blockchain Nodes]
  LED[(Internal Ledger)]
  U --> ME --> LED
  U --> WAL --> CHN
  WAL --- CW

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class U client;
    class ME,WAL,CW,CHN service;
    class LED datastore;