title: find four elements in array whose sum equal to a given number X
body: <p>I need help to find an algorithm that finds:</p>
  
  <ul>
  <li>four elements in array</li>
  <li>whose sum equal to a given number X</li>
  <li>in O(n^2*log(n))</li>
  </ul>
  
  <p>prefer in pseudo-code or c,c++</p>