Short Arrays:

Array = randi(10,1,randi(6,1,1)+4)-5

This command will generate an array which you should be able to evaluate by hand (and also have your code evaluate for testing purposes).

Long Arrays:

Array = randi(200,1,randi(500,1,1)+50)-100

This command will generate an array which will be too large to evaluate by hand, but which your code should still work with.

Sort the given array 

Remove the repeated values (as asked for extra credit)

Intialize solution vector

Find the last negative element in shorted array , assume its index be last_n

Outer loop

  From 1^st element up to last negative element

       First atom  = array(I,i)

          Inner loop

              From last element to first positive element in array

                     Second atom = array (1,j)

                     Find the third element

                            Third element = 0- (first atom + second atom)

                            Check (third_elemnt <= second atom) % this step is to avoid repetition of same solution

                                           Search the element inarray

                                            If it is present add this to solution vector

                     Else proceed for next iteration

            Close inner loop

Close outer loop

Advantage now there are no repeated results , the number of loops has been reduced using the algorithm.

Example

Input array   = [5    -3     5     2    -4    -2     1     5     5  0]

sorted array =   -4    -3    -2     0     1     2     5     5     5     5 

Unique array and sorted = -4    -3    -2     0     1     2     5

Index of last negative number =3

Outer loop  i=1:1:3

Inner loop  j =7:-1:5

Output

sol =

    -4     2     2

    -3     5    -2

    -3     2     1

    -2     5    -3

    -2     2     0

    -2     1     1

There are no repeated solution

Each vector  is unique.