Array

Contiguous memory, O(1) random access.

array

length 5

[0]

[1]

[2]

[3]

[4]

Arrays give O(1) access by index — the address is pure math.

tap a cell to access · ✕ to delete

How it works

An array stores elements in one continuous block of memory. Because every slot is the same size, the address of any index is pure arithmetic — base + i × size — giving constant-time access. The trade-off: inserting or deleting in the middle shifts everything after it.

Mental models

Index access is math, not a search — base address plus offset.
Cache-friendly: contiguous layout means the CPU prefetches neighbors.
Dynamic arrays double capacity on overflow → amortized O(1) appends.

Common pitfalls

Inserting at the front is O(n) — every element shifts right.
Resizing copies the whole array; a single append can briefly be O(n).

Complexity

Access: O(1)
Search: O(n)
Insert (end): O(1)*amortized for dynamic arrays
Insert (middle): O(n)shifts elements
Delete: O(n)
Space: O(n)

Reach for it when

You know the size up front or it grows mostly at the end.
You need fast index lookups and tight memory locality.