title: Subsequence sum
body: <p>Given an array of integers eg <code>[1, 2, -3, 1]</code> find whether there is a sub-sequence that sums to <code>0</code> and return it (eg <code>[1, 2, -3]</code> or <code>[2, -3, 1]</code>).<br>
  Checking every sub-sequence is <code>O(n^2)</code> which is too inefficient. Any idea for improvements?</p>