Arrays and dynamic arrays

Arrays give indexed access and cache-friendly sequential scans. Dynamic arrays reserve capacity and resize when needed, so append is usually constant time but occasionally copies many elements. JavaScript arrays are higher-level objects, yet interview reasoning still uses array access, scan, insert, and delete costs.

On interviews: Expect tasks around two pointers, prefix sums, in-place mutation, stable order, and when a simple scan beats a more complex structure.

Common pitfalls: Insertion at the front shifts elements. Sparse JavaScript arrays and mutation during iteration can surprise you. Clarify whether the input may be sorted, mutated, or contain duplicates before optimizing.

Checklist:

• Use indexes deliberately.
• Mention resize cost for dynamic arrays.
• Clarify mutation rules.
• Test empty and one-element inputs.