title: Split an array into four sub-array
body: <blockquote>
    <p>Given an array, it contains N element, which are all positive integers; if we can  find <strong>three</strong> elements, and they divide the array into four parts (<strong>Notice: the three elements are not contained in any part of the four</strong>), and the sum of each part are equal, then we call the array a "balanced" array. Design an algorithm to judge whether an array is balance, with limit: Time O(N), Space O(N).</p>
  </blockquote>
  
  <p>Here is an example:</p>
  
  <pre><code>a = [1,7,4,2,6,5,4,2,2,9,8];
  b = [1,8,10,5,3,1,2,3]
  </code></pre>
  
  <p>a is balanced, 'cause the element 4, 5, 9 divide the array into <code>[1,7], [2,6], [4,2,2], [8]</code>, the sum of each is 8.
  <code>b</code> is not balanced, because we can not find a solution.</p>
  
  <p>Any idea is appreciated!</p>