<p>You are given a string <code>s</code>. We want to partition the string into as many parts as possible so that each letter appears in at most one part.</p>
<p>Note that the partition is done so that after concatenating all the parts in order, the resultant string should be <code>s</code>.</p>
<p>Return <em>a list of integers representing the size of these parts</em>.</p>