Three trades that net to zero

A list of signed trade quantities is given (positive for buys, negative for sells). Return every distinct triple of values that sums to zero, with no duplicate triples in the output. For example, $[-1, 0, 1, 2, -1, -4, 3]$ gives $(-4, 1, 3)$, $(-1, -1, 2)$ and $(-1, 0, 1)$. Beat the $O(n^3)$ brute force.