Given an array nums of $n$ integers, return an array of all the unique quadruplets, [nums[a], nums[b], nums[c], nums[d]] such that:

• $0 \leq$ a, b, c, d $< n$

• a, b, c, and d are distinct.

• nums[a] + nums[b] + nums[c] + nums[d] $=$ target

You may return the answer in any order.

Constraints:

• $1 \leq$ nums.length ...