Dynamic Array Theory

Array with automatic resizing

A dynamic array is an array with a big improvement: automatic resizing.

One limitation of arrays is that they're fixed size, meaning you need to specify the number of elements your array will hold ahead of time.

A dynamic array expands as you add more elements. So you don't need to determine the size ahead of time.

Strengths:

Fast lookups. Just like arrays, retrieving the element at a given index takes O(1) time.

O(1)
Variable size. You can add as many items as you want, and the dynamic array will expand to hold them.
Cache-friendly. Just like arrays, dynamic arrays place items right next to each other in memory, making efficient use of caches.
Allows nulls values
Allows duplicate elements

Weaknesses:

Slow worst-case appends. Usually, adding a new element at the end of the dynamic array takes O(1) time. But if the dynamic array doesn't have any room for the new item, it need to be resized, which takes O(n) time.
Costly inserts and deletes. Just like arrays, elements are stored adjacent to each other. So adding or removing an item in the middle of the array requires to rearrange items in array, which again take O(n) time.