<p>Given an integer array <code>nums</code> and two integers <code>firstLen</code> and <code>secondLen</code>, return <em>the maximum sum of elements in two non-overlapping <strong>subarrays</strong> with lengths </em><code>firstLen</code><em> and </em><code>secondLen</code>.</p>
<p>The array with length <code>firstLen</code> could occur before or after the array with length <code>secondLen</code>, but they have to be non-overlapping.</p>
<p>A <strong>subarray</strong> is a <strong>contiguous</strong> part of an array.</p>