> For the complete documentation index, see [llms.txt](https://edsonha.gitbook.io/my-gitbook/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://edsonha.gitbook.io/my-gitbook/data-structure-and-algorithm/array.md).

# Array

Organize items sequentially.

* lookup O(1)  - search item, for example array\[0]
* append:
* * push O(1) - Add at the end of the array:
  * pop O(1) - Remove the last item of the array
* insert: 
* * unshift O(n) - Insert at the start of the array
* delete:
* * splice O(n) - Insert or delete 

There are two types of array:

1. Static array - the length of an array or the size is predetermined, like in Java
2. Dynamic array - the size of an array is not predetermined. If you need to add data, the array will be rebuilt at a new location with more memory. That is why the append can be O(n) because it need to loop all over again to rebuild the array