Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

` ````
#For example, given array
S = [-1, 0, 1, 2, -1, -4]
#A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]
]
```

Note:

The solution set must not contain duplicate triplets.