title: Need to generate superset in java
body: <p>Trying to figure out a way to generate a superset using java
  need simple answer to</p>
  
  <p>what am looking for is</p>
  
  <p>Input : <code>ab</code></p>
  
  <p>Output : <code>{} {a} {b} {ab}</code></p>
  
  <p>how do i go about this any clue ?</p>
  
  <p>Thanks in advance</p>