Data Structures & Complexity — Simple

flowchart LR
  C[O 1 - constant]
  L[O log n - log]
  N[O n - linear]
  NL[O n log n - linearithmic]
  N2[O n^2 - quadratic]
  E[O 2^n - exponential]
  C --> L --> N --> NL --> N2 --> E

  classDef g fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
  classDef y fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
  classDef r fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
  class C,L g;
  class N,NL y;
  class N2,E r;

    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 C,L,N,NL,N2,E service;

A quick reference: time + space costs for the data structures you'll reach for in any LLD problem. Pick by the operation you do most, not by what feels familiar.