Remove Duplicates From an Array / Sorted Array

Question

## Problem

Remove duplicates in place from a sorted array and return the new length; then discuss the unsorted-array variant.

## Example
```
[1,1,2,3,3] -> [1,2,3], length 3
```

## Constraints
- 0 ≤ n ≤ 3 × 10^4

## Approach
Two-pointer write index for sorted; hash set for unsorted. Discuss the space trade-off.